01428nas a2200205 4500008004100000245008900041210006900130260000800199300001000207490000700217520073100224100002600955700002600981700002101007700002301028700002101051700001701072700001901089856011401108 2008 eng d00aIntroduction to the density matrix renormalization group ansatz in quantum chemistry0 aIntroduction to the density matrix renormalization group ansatz  cJAN a49-650 v183 aThe Density Matrix Renormalisation Group (DMRG) is an electronic structure method that has recently been applied to ab-initio quantum chemistry. Even at this early stage, it has enabled the solution of many problems that would previously have been intractable with any other method, in particular, multireference problems with very large active spaces. Historically, the DMRG was not originally formulated from a wavefunction perspective, but rather in a Renormalisation Group (RG) language. However, it is now realised that a wavefunction view of the DMRG provides a more convenient, and in some cases more powerful, paradigm. Here we provide an expository introduction to the DMRG ansatz in the context of quantum chemistry.1 aChan, Garnet, Kin-Lic1 aDorando, Jonathan, J.1 aGhosh, Debashree1 aHachmann, Johannes1 aNeuscamman, Eric1 aWang, Haitao1 aYanai, Takeshi uhttps://library.ncl.res.in/content/introduction-density-matrix-renormalization-group-ansatz-quantum-chemistry00603nas a2200145 4500008004100000245011600041210006900157260000800226490000800234100002100242700002300263700001900286700002600305856012600331 2008 eng d00aOrbital optimization in the density matrix renormalization group, with applications to polyenes and ss-carotene0 aOrbital optimization in the density matrix renormalization group cAPR0 v1281 aGhosh, Debashree1 aHachmann, Johannes1 aYanai, Takeshi1 aChan, Garnet, Kin-Lic uhttps://library.ncl.res.in/content/orbital-optimization-density-matrix-renormalization-group-applications-polyenes-and-ss01939nas a2200169 4500008004100000245012400041210006900165260000800234300001400242490000800256520129700264100001901561700002001580700002101600700002601621856012201647 2009 eng d00aAccelerating convergence in iterative solution for large-scale complete active space self-consistent-field calculations0 aAccelerating convergence in iterative solution for largescale co cAUG a2178-21900 v1093 aAn algorithm that accelerates the convergence of the iterative optimization of the complete active space self-consistent field (CASSCF) wavefunction so as to find a optimum solution in fewer macroiterations is described. The algorithm is oriented to large-scale CASSCF problems that are to be solved with a combination of density matrix renormalization group (DMRG) method for the configuration interaction (CI) process. The algorithm is based on the alternating (or two-step) CASSCF optimization in which the CI and molecular orbital (MO) parameters are optimized separately. Convergence ratio is improved by finding further optimized MOs from a linear extrapolation of the MO sets of the iteration history. The acceleration results in fewer diagonalizations in a total CASSCF calculation to save a considerable computational cost. The convergence performance is examined in a couple of realistic applications on SiC(3) and poly (phenyl)carbenes. For poly(phenyl)carbenes, the large-size CASSCF calculations with CAS(30e,30o) that entails full pi valence space as well as sp(2) orbital space of carbenes are performed by using the practical implementation of DMRG-CASSCF in conjunction with the acceleration technique. (C) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 109: 2178-2190, 20091 aYanai, Takeshi1 aKurashige, Yuki1 aGhosh, Debashree1 aChan, Garnet, Kin-Lic uhttps://library.ncl.res.in/content/accelerating-convergence-iterative-solution-large-scale-complete-active-space-self01255nas a2200169 4500008004100000245009400041210006900135260000800204300002700212490000800239520062800247100001900875700002100894700002100915700002600936856012300962 2009 eng d00aStudy of cumulant approximations to n-electron valence multireference perturbation theory0 aStudy of cumulant approximations to nelectron valence multirefer cMAY aArticle Number: 1941070 v1303 aWe investigate the possibility of reducing the complexity of multireference perturbation theory through cumulant based approximations to the high-order density matrices that appear in such theories. Our test cases show that while the cumulant approximated forms are degraded in accuracy relative to the parent theory and exhibit intruder state problems that must be carefully handled, they may provide a route to a simple estimation of dynamic correlation when the parent perturbation theory is infeasible. Nonetheless, further work is clearly needed on better approximations to the denominators in the perturbation theory.1 aZgid, Dominika1 aGhosh, Debashree1 aNeuscamman, Eric1 aChan, Garnet, Kin-Lic uhttps://library.ncl.res.in/content/study-cumulant-approximations-n-electron-valence-multireference-perturbation-theory01741nas a2200217 4500008004100000245015100041210006900192260000800261490000800269520090500277100002101182700002101203700002301224700003001247700002201277700002101299700002501320700002901345700002101374856012801395 2010 eng d00aNon-covalent interactions in extended systems described by the effective fragment potential method: theory and application to nucleobase oligomers0 aNoncovalent interactions in extended systems described by the ef cNOV0 v1143 aThe implementation of the effective fragment potential (EFP) method within the Q-CHEM electronic structure package is presented. The EFP method is used to study noncovalent π-π and hydrogen-bonding interactions in DNA strands. Since EFP is a computationally inexpensive alternative to high-level ab initio calculations, it is possible to go beyond the dimers of nucleic acid bases and to investigate the asymptotic behavior of different components of the total interaction energy. The calculations demonstrated that the dispersion energy is a leading component in π-stacked oligomers of all sizes. Exchange-repulsion energy also plays an important role. The contribution of polarization is small in these systems, whereas the magnitude of electrostatics varies. Pairwise fragment interactions (i.e., the sum of dimer binding energies) were found to be a good approximation for the oligomer energy.1 aGhosh, Debashree1 aKosenkov, Dmytro1 aVanovschi, Vitalii1 aWilliams, Christopher, F.1 aHerbert, John, M.1 aGordon, Mark, S.1 aSchmidt, Michael, W.1 aSlipchenko, Lyudmila, V.1 aKrylov, Anna, I. uhttps://library.ncl.res.in/content/non-covalent-interactions-extended-systems-described-effective-fragment-potential-method01831nas a2200181 4500008004100000245010100041210006900142260000800211300001600219490000600235520117900241100002401420700002101444700001901465700001901484700002101503856012501524 2011 eng d00aCorrection to what drives the redox properties of model green fluorescence protein chromophores?0 aCorrection to what drives the redox properties of model green fl cOCT a2695–26950 v23 a

We report the first experimental determination of the oxidation potentials E-ox(0). (relative to the standard hydrogen electrode, SHE) of model green fluorescent protein (GFP) chromophores. Para-, meta, and ortho-hydroxy (4-hydroxybenzylidene-2,3-dimethylimidazolinone, HBDI) and methoxy (MeOBDI) derivatives were studied. E-ox(0) of the three isomers in acetonitrile are -1.31, -1.52, and -1.39 V, respectively. Electronic structure calculations reproduce the observed differences between the isomers and reveal that E-ox(0) follows the ionization energies (IEs), that is, p-MeOBDI has the lowest IE (6.96 eV in the gas phase) due to resonance stabilization of its cation, whereas the resonance is detuned in m-MeOBDL resulting in more-negative E-ox(0). The observed meta and ortho effects in E-ox(0) are similar to the trends in pK(a). The effect of increased solvent polarity on absolute.E-ox(0) (and especially on para-meta-ortho differences) was found to be small. The redox properties of GFP chromophores are driven by their structure and can be correlated with IEs, which can be exploited in predicting the properties of other fluorescent protein chromophores.

1 aSolntsev, Kyril, M.1 aGhosh, Debashree1 aAmador, Adrian1 aJosowicz, Mira1 aKrylov, Anna, I. uhttps://library.ncl.res.in/content/correction-what-drives-redox-properties-model-green-fluorescence-protein-chromophores02027nas a2200169 4500008004100000245009800041210006900139260000800208300001400216490000800230520141600238100002101654700002101675700002901696700002101725856011101746 2011 eng d00aEffect of solvation on the vertical ionization energy of thymine: from microhydration to bulk0 aEffect of solvation on the vertical ionization energy of thymine cJUN a6028-60380 v1153 aThe effect of hydration on the vertical ionization energy (VIE) of thymine was characterized using equation-of-motion ionization potential coupled-cluster (EOM-IP-CCSD) and effective fragment potential (EFP) methods. We considered several microsolvated clusters as well as thymine solvated in bulk water. The VIE in bulk water was computed by averaging over solvent-solute configurations obtained from equilibrium molecular dynamics trajectories at 300 K. The effect of microsolvation was analyzed and contrasted against the combined effect of the first solvation shell in bulk water. Microsolvation reduces the ionization energy (IE) by about 0.1 eV per water molecule, while the first solvation shell increases the IE by 0.1 eV. The subsequent solvation lowers the IE, and the bulk value of the solvent-induced shift of thymine's VIE is approximately -0.9 eV. The combined effect of the first solvation shell was explained in terms of specific solute-solvent interactions, which were investigated using model structures. The convergence of LE to the bulk value requires the hydration sphere of approximately 13.5 angstrom radius. The performance of the EOM-IP-CCSD/EFP scheme was benchmarked against full EOM-IP-CCSD using microhydrated structures. The errors were found to be less than 0.01-0.02 eV. The relative importance of the polarization and higher multipole moments in EFP model was also investigated.1 aGhosh, Debashree1 aIsayev, Olexandr1 aSlipchenko, Lyudmila, V.1 aKrylov, Anna, I. uhttps://library.ncl.res.in/content/effect-solvation-vertical-ionization-energy-thymine-microhydration-bulk01771nas a2200169 4500008004100000245008700041210006900128260000800197490000600205520117200211100002401383700002101407700001901428700001901447700002101466856011401487 2011 eng d00aWhat drives the redox properties of model green fluorescence protein chromophores?0 aWhat drives the redox properties of model green fluorescence pro cSEP0 v23 aWe report the first experimental determination of the oxidation potentials E-ox(0). (relative to the standard hydrogen electrode, SHE) of model green fluorescent protein (GFP) chromophores. Para-, meta, and ortho-hydroxy (4-hydroxybenzylidene-2,3-dimethylimidazolinone, HBDI) and methoxy (MeOBDI) derivatives were studied. E-ox(0) of the three isomers in acetonitrile are -1.31, -1.52, and -1.39 V, respectively. Electronic structure calculations reproduce the observed differences between the isomers and reveal that E-ox(0) follows the ionization energies (IEs), that is, p-MeOBDI has the lowest IE (6.96 eV in the gas phase) due to resonance stabilization of its cation, whereas the resonance is detuned in m-MeOBDL resulting in more-negative E-ox(0). The observed meta and ortho effects in E-ox(0) are similar to the trends in pK(a). The effect of increased solvent polarity on absolute.E-ox(0) (and especially on para-meta-ortho differences) was found to be small. The redox properties of GFP chromophores are driven by their structure and can be correlated with IEs, which can be exploited in predicting the properties of other fluorescent protein chromophores.1 aSolntsev, Kyril, M.1 aGhosh, Debashree1 aAmador, Adrian1 aJosowicz, Mira1 aKrylov, Anna, I. uhttps://library.ncl.res.in/content/what-drives-redox-properties-model-green-fluorescence-protein-chromophores01868nas a2200193 4500008004100000245017200041210006900213260000800282300001400290490000800304520112600312100002101438700001701459700001901476700001801495700002301513700002101536856011701557 2012 eng d00aFirst-principle protocol for calculating ionization energies and redox potentials of solvatedmolecules and ions: theory and application to aqueous phenol and phenolate0 aFirstprinciple protocol for calculating ionization energies and  cJUN a7269-72800 v1163 aThe effect of hydration on the lowest vertical ionization energy (VIE) of phenol and phenolate solvated in bulk water was characterized using the equation-of-motion ionization potential coupled-cluster (EOM-IP-CCSD) and effective fragment potential (EFP) methods (referred to as EOM/EFP) and determined experimentally by valence photoemission measurements using microjets and synchrotron radiation. The computed solvent-induced shifts in VIEs (Delta VIEs) are 0.66 and +5.72 eV for phenol and phenolate, respectively. Our best estimates of the absolute values of VIEs (7.9 and 7.7 eV for phenol and phenolate) agree reasonably well with the respective experimental values (7.8 +/- 0.1 and 7.1 +/- 0.1 eV). The EOM/EFP scheme was benchmarked against full EOM-IP-CCSD using microsolvated phenol and phenolate clusters. A protocol for calculating redox potentials with EOM/EFP was developed based on linear response approximation (LRA) of free energy determination. The oxidation potentials of phenol and phenolate calculated using LRA and EOM/EFP are 1.32 and 0.89 V, respectively; they agree well with experimental values.1 aGhosh, Debashree1 aRoy, Anirban1 aSeidel, Robert1 aWinter, Bernd1 aBradforth, Stephen1 aKrylov, Anna, I. uhttps://library.ncl.res.in/content/first-principle-protocol-calculating-ionization-energies-and-redox-potentials02058nas a2200169 4500008004100000245018900041210006900230260000800299300001600307490000800323520134500331100002101676700001901697700002301716700002101739856012801760 2012 eng d00aToward understanding the redox properties of model chromophores from the greenfluorescent protein family: an interplay between conjugation, resonance stabilization, and solvent effects0 aToward understanding the redox properties of model chromophores  cOCT a12398-124050 v1163 aThe redox properties of model chromophores from the green fluorescent protein family are characterized computationally using density functional theory with a long-range corrected functional, the equation-of-motion coupled-cluster method, and implicit solvation models. The analysis of electron-donating abilities of the chromophores reveals an intricate interplay between the size of the chromophore, conjugation, resonance stabilization, presence of heteroatoms, and solvent effects. Our best estimates of the gas-phase vertical/adiabatic detachment energies of the deprotonated (i.e., anionic) model red, green, and blue chromophores are 3.27/3.15, 2.79/2.67, and 2.75/2.35 eV, respectively. Vertical/adiabatic ionization energies of the respective protonated (i.e., neutral) species are 7.64/7.35, 7.38/7.15, and 7.70/7.32 eV, respectively. The standard reduction potentials (E-red(0)) of the anionic (Chr(center dot)/Chr(-)) and neutral (Chr(+center dot)/Chr) model chromophores in acetonitrile are 0.34/1.40 V (red), 0.22/1.24 V (green), and -0.12/1.02 V (blue), suggesting, counterintuitively, that the red chromophore is more difficult to oxidize than the green and blue ones (in both neutral and deprotonated forms). The respective redox potentials in water follow a similar trend but are more positive than the acetonitrile values.1 aGhosh, Debashree1 aAcharya, Atanu1 aTiwari, Subodh, C.1 aKrylov, Anna, I. uhttps://library.ncl.res.in/content/toward-understanding-redox-properties-model-chromophores-greenfluorescent-protein-family01658nas a2200181 4500008004100000245011100041210006900152260000800221300001200229490000600241520099300247100002101240700001601261700002701277700002101304700001901325856013201344 2012 eng d00aVUV Photoionization and Ab initio determination of the ionization energy of a gas-phasesugar (deoxyribose)0 aVUV Photoionization and Ab initio determination of the ionizatio cJAN a 97-1010 v33 aThe ionization energy of gas-phase deoxyribose was determined using tunable vacuum ultraviolet synchrotron radiation coupled to an effusive thermal source. Adiabatic and vertical ionization energies of the ground and first four excited states of alpha-pyranose, the structure that dominates in the gas phase, were calculated using high-level electronic structure methods. An appearance energy of 9.1(+/- 0.05) eV was recorded, which agrees reasonably well with a theoretical value of 8.8 eV for the adiabatic ionization energy. A clear picture of the dissociative photoionization dynamics of deoxyribose emerges from the fragmentation pattern recorded using mass spectrometry and from ab initio molecular dynamics calculations. The experimental threshold 9.4 (+/- 0.05) eV for neutral water elimination upon ionization is captured well in the calculations, and qualitative insights are provided by molecular orbital analysis and molecular dynamics snapshots along the reaction coordinate.1 aGhosh, Debashree1 aGolan, Amir1 aTakahashi, Lynelle, K.1 aKrylov, Anna, I.1 aAhmed, Musahid uhttps://library.ncl.res.in/content/vuv-photoionization-and-ab-initio-determination-ionization-energy-gas-phasesugar-deoxyribose02542nas a2200349 4500008004100000022001400041245008400055210006900139260006700208300001400275490000700289520144400296653003301740653001601773653001401789653001001803653000701813653001701820653002901837653001101866653001001877100002101887700002101908700002301929700001801952700001801970700001601988700002702004700002102031700002902052856011102081 2013 eng d a0192-865100aEffective fragment potential method in Q-CHEM: a guide for users and developers0 aEffective fragment potential method in QCHEM a guide for users a a111 RIVER ST, HOBOKEN 07030-5774, NJ USAbWILEY-BLACKWELLcMAY a1060-10700 v343 a

A detailed description of the implementation of the effective fragment potential (EFP) method in the Q-CHEM electronic structure package is presented. The Q-CHEM implementation interfaces EFP with standard quantum mechanical (QM) methods such as HartreeFock, density functional theory, perturbation theory, and coupled-cluster methods, as well as with methods for electronically excited and open-shell species, for example, configuration interaction, time-dependent density functional theory, and equation-of-motion coupled-cluster models. In addition to the QM/EFP functionality, a fragment-only feature is also available (when the system is described by effective fragments only). To aid further developments of the EFP methodology, a detailed description of the C++ classes and EFP module's workflow is presented. The EFP input structure and EFP job options are described. To assist setting up and performing EFP calculations, a collection of Perl service scripts is provided. The precomputed EFP parameters for standard fragments such as common solvents are stored in Q-CHEM's auxiliary library; they can be easily invoked, similar to specifying standard basis sets. The instructions for generating user-defined EFP parameters are given. Fragments positions can be specified by their center of mass coordinates and Euler angles. The interface with the IQMOL and WEBMO software is also described. (c) 2013 Wiley Periodicals, Inc.

10aeffective fragment potential10aEFP library10ahybrid QM10aIQMOL10aMM10amodular code10anonempirical force field10aQ-CHEM10aWEBMO1 aGhosh, Debashree1 aKosenkov, Dmytro1 aVanovschi, Vitalii1 aFlick, Joanna1 aKaliman, Ilya1 aShao, Yihan1 aGilbert, Andrew, T. B.1 aKrylov, Anna, I.1 aSlipchenko, Lyudmila, V. uhttps://library.ncl.res.in/content/effective-fragment-potential-method-q-chem-guide-users-and-developers-001670nas a2200169 4500008004100000022001400041245012200055210006900177260012500246300001100371490000800382520091700390100002701307700001601334700002101350856012901371 2013 eng d a0021-960600aPerturbative approximations to single and double spin flip equation of motion coupled cluster singles doubles methods0 aPerturbative approximations to single and double spin flip equat aCIRCULATION & FULFILLMENT DIV, 2 HUNTINGTON QUADRANGLE, STE 1 N O 1, MELVILLE, NY 11747-4501 USAbAMER INST PHYSICScSEP a1241160 v1393 a

Spin flip equation of motion coupled cluster (EOM-SF-CC) can correctly treat situations involving electronic degeneracies or near degeneracies, e. g., bond breaking, di- and tri-radicals, etc. However, for large systems EOM-SF-CC (even in single and double excitations) is computationally prohibitively expensive. Therefore, earlier approximations to EOM-SF-CC methods such as spin flip configuration interaction singles with perturbative doubles (SF-CIS(D)) have been proposed. In this work, we present a new perturbative approximation to EOM-SF-CC, which has been found to be more accurate than SF-CIS(D). The capabilities, advantages, and timings of the new approach have been demonstrated considering the singlet-triplet gaps in di- and triradicals as well as bond breaking examples. The method is extended to double spin flip EOM-CC and its capabilities have been tested. (C) 2013 AIP Publishing LLC.

1 aDutta, Achintya, Kumar1 aPal, Sourav1 aGhosh, Debashree uhttps://library.ncl.res.in/content/perturbative-approximations-single-and-double-spin-flip-equation-motion-coupled-cluster-001195nas a2200193 4500008004100000022001400041245008700055210006900142260011000211300001600321490000700337520043600344100001600780700002700796700001600823700002100839700002000860856012100880 2014 eng d a1463-907600aElectrostatics determine vibrational frequency shifts in hydrogen bonded complexes0 aElectrostatics determine vibrational frequency shifts in hydroge aTHOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLANDbROYAL SOC CHEMISTRYcOCT a25247-252500 v163 a

The red-shifts in the acetylenic C-H stretching vibration of C-H center dot center dot center dot X (X = O, N) hydrogen-bonded complexes increase with an increase in the basicity of the Lewis base. Analysis of various components of stabilization energy suggests that the observed red-shifts are correlated with the electrostatic component of the stabilization energy, while the dispersion modulates the stabilization energy.

1 aDey, Arghya1 aMondal, Sohidul, Islam1 aSen, Saumik1 aGhosh, Debashree1 aPatwari, Naresh uhttps://library.ncl.res.in/content/electrostatics-determine-vibrational-frequency-shifts-hydrogen-bonded-complexes-002001nas a2200157 4500008004100000022001400041245007500055210006900130260007100199300001400270490000800284520140900292100001501701700002101716856010601737 2014 eng d a1089-563900aIonization-induced tautomerization in cytosine and effect of solvation0 aIonizationinduced tautomerization in cytosine and effect of solv a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcJUL a5323-53320 v1183 a

The recent observation of excitation-induced tautomerization in gas-phase cytosine motivated us to investigate the possibility of facile tautomerization in ionized cytosine and the effect of solvation on the tautomerization barriers. The tautomerization mechanisms were characterized at the density functional theory (DFT)omega B97X-D and coupled-cluster singles and doubles (CCSD) levels of theory. Vertical and adiabatic ionization energies (VIEs and AIEs, respectively) of the tautomers of cytosine and the microsolvated species were calculated with the equation-of-motion ionization-potential coupled-cluster (EOM-IP-CCSD) method. We observed that, in microsolvated cytosine, the solvatochromic shifts of the VIEs can be both blue- and red-shifted depending on the tautomers. This is explained by the analysis of the charge dipole interactions between the cytosine and water molecules. We noticed that, upon ionization, gas-phase tautomerization barriers are reduced by 0-4 kcal/mol, whereas microsolvated (with one water) tautomerization barriers are reduced by 4-5 kcal/mol. We also investigated the tautomerization process in solvation using a continuum model with one active water molecule in the quantum mechanical region. We noticed that, even though bulk solvation has a significant effect on ionization energies, its effect on the ionization-induced tautomerization barrier is minimal.

1 aDas, Tamal1 aGhosh, Debashree uhttps://library.ncl.res.in/content/ionization-induced-tautomerization-cytosine-and-effect-solvation-001735nas a2200145 4500008004100000022001400041245011200055210006900167260008700236300001100323490000800334520110100342100002101443856012501464 2014 eng d a0021-960600aPerturbative approximation to hybrid equation of motion coupled cluster/effective fragment potential method0 aPerturbative approximation to hybrid equation of motion coupled  a1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USAbAMER INST PHYSICScMAR a0941010 v1403 a

Hybrid quantum mechanics/molecular mechanics (QM/MM) methods provide an attractive way to closely retain the accuracy of the QM method with the favorable computational scaling of the MM method. Therefore, it is not surprising that QM/MM methods are being increasingly used for large chemical/biological systems. Hybrid equation of motion coupled cluster singles doubles/effective fragment potential (EOM-CCSD/EFP) methods have been developed over the last few years to understand the effect of solvents and other condensed phases on the electronic spectra of chromophores. However, the computational cost of this approach is still dominated by the steep scaling of the EOM-CCSD method. In this work, we propose and implement perturbative approximations to the EOM-CCSD method in this hybrid scheme to reduce the cost of EOM-CCSD/EFP. The timings and accuracy of this hybrid approach is tested for calculation of ionization energies, excitation energies, and electron affinities of microsolvated nucleic acid bases (thymine and cytosine), phenol, and phenolate. (C) 2014 AIP Publishing LLC.

1 aGhosh, Debashree uhttps://library.ncl.res.in/content/perturbative-approximation-hybrid-equation-motion-coupled-clustereffective-fragment-002230nas a2200253 4500008004100000245008600041210006900127260000800196300001200204490000800216520142300224100001601647700001901663700002401682700002701706700002001733700002001753700002201773700001701795700001401812700001801826700002101844856011101865 2015 eng d00aAdvances in molecular quantum chemistry contained in the Q-Chem 4 program package0 aAdvances in molecular quantum chemistry contained in the QChem 4 cJAN a184-2150 v1133 a

A summary of the technical advances that are incorporated in the fourth major release of the Q-Chem quantum chemistry program is provided, covering approximately the last seven years. These include developments in density functional theory methods and algorithms, nuclear magnetic resonance (NMR) property evaluation, coupled cluster and perturbation theories, methods for electronically excited and open-shell species, tools for treating extended environments, algorithms for walking on potential surfaces, analysis tools, energy and electron transfer modelling, parallel computing capabilities, and graphical user interfaces. In addition, a selection of example case studies that illustrate these capabilities is given. These include extensive benchmarks of the comparative accuracy of modern density functionals for bonded and non-bonded interactions, tests of attenuated second order Moller-Plesset (MP2) methods for intermolecular interactions, a variety of parallel performance benchmarks, and tests of the accuracy of implicit solvation models. Some specific chemical examples include calculations on the strongly correlated Cr-2 dimer, exploring zeolite-catalysed ethane dehydrogenation, energy decomposition analysis of a charged ter-molecular complex arising from glycerol photoionisation, and natural transition orbitals for a Frenkel exciton state in a nine-unit model of a self-assembling nanotube.

1 aShao, Yihan1 aGan, Zhengting1 aEpifanovsky, Evgeny1 aGilbert, Andrew, T. B.1 aWormit, Michael1 aKussmann, Joerg1 aLange, Adrian, W.1 aBehn, Andrew1 aDeng, Jia1 aFeng, Xintian1 aGhosh, Debashree uhttps://library.ncl.res.in/content/advances-molecular-quantum-chemistry-contained-q-chem-4-program-package01648nas a2200181 4500008004100000022001400041245008600055210006900141260007100210300001600281490000800297520096300305100002001268700001501288700002601303700002101329856011601350 2015 eng d a1520-610600aFeasibility of ionization-mediated pathway for ultraviolet-induced melanin damage0 aFeasibility of ionizationmediated pathway for ultravioletinduced a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcOCT a13288-132930 v1193 a

Melanin is the pigment found in human skin that is responsible for both photoprotection and photodamage. Recently there have been reports that greater photodamage of DNA occurs when cells containing melanin are irradiated with ultraviolet (UV) radiation, thus suggesting that the photoproducts of melanin cause DNA damage. Photoionization processes have also been implicated in the photodegradation of melanin. However, not much is known about the oxidation potential of melanin and its monomers. In this work we calculate the ionization energies of monomers, dimers, and few oligomers of eumelanin to estimate the threshold energy required for the ionization of eumelanin. We find that this threshold is within the UV-B region for eumelanin. We also look at the charge and spin distributions of the various ionized states of the monomers that are formed to understand which of the ionization channels might favor monomerization from a covalent dimer.

1 aMandal, Mukunda1 aDas, Tamal1 aGrewal, Baljinder, K.1 aGhosh, Debashree uhttps://library.ncl.res.in/content/feasibility-ionization-mediated-pathway-ultraviolet-induced-melanin-damage-001828nas a2200157 4500008004100000022001400041245013300055210006900188260011000257300001400367490000700381520110800388100002301496700002101519856013001540 2015 eng d a1463-907600aSinglet-triplet gaps in polyacenes: a delicate balance between dynamic and static correlations investigated by spin-flip methods0 aSinglettriplet gaps in polyacenes a delicate balance between dyn aTHOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLANDbROYAL SOC CHEMISTRYcMAR a9849-98560 v173 a

Over the last few years people have been interested in the process of singlet fission, owing to its relevance to solar cell technology. The energetics of singlet fission is intimately related to singlet-triplet (ST) gaps and energies of singlet excited states. However, accurate calculations of ST gaps in polyacenes are complicated due to near degeneracies in the pi orbitals, and therefore, have been quite challenging. The spin-flip equation-of-motion coupled-cluster (SF-EOM-CC) and its perturbative approximation have been shown to correctly treat situations involving electronic degeneracies and near degeneracies. In this work, we use various spin-flip methods to benchmark the ST gaps of small polyacenes and show that the error in the ST gaps with respect to the experiment is small and does not increase appreciably with the system size. The diradical and polyradical character of the polyacene ground states increase with the system size. However, for the small polyacenes the open-shell character of the ground state is still small enough to be treated using single reference methods.

1 aIbeji, Collins, U.1 aGhosh, Debashree uhttps://library.ncl.res.in/content/singlet-triplet-gaps-polyacenes-delicate-balance-between-dynamic-and-static-correlations-002501nas a2200193 4500008004100000022001400041245024300055210006900298260011000367300001200477490000700489520158500496100002702081700001602108700001602124700002002140700002102160856012602181 2015 eng d a1463-907600aSpectroscopic and ab initio investigation of 2,6-difluorophenylacetylene-amine complexes: coexistence of C-H center dot center dot center dot N and lone-pair center dot center dot center dot pi complexes and intermolecular coulombic decay0 aSpectroscopic and ab initio investigation of 26difluorophenylace aTHOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLANDbROYAL SOC CHEMISTRYcOCT a434-4430 v173 a

Binary complexes of 2,6-difluorophenylacetylene with methylamine, dimethylamine, trimethylamine and triethylamine were investigated using one colour resonant two photon ionization and infrared-optical double resonance spectroscopic techniques combined with high level ab initio calculations. All four amines form C-Ac-H center dot center dot center dot N hydrogen-bonded complexes. Additionally trimethylamine and triethylamine form complexes characterized by Lp center dot center dot center dot pi interactions, due to the electron deficient nature of the phenyl ring of 2,6-difluorophenylacetylene. The Lp center dot center dot center dot pi interacting structure of the 2,6-difluorophenylacetylenetrimethylamine complex is about 1.5 kJ mol(-1) higher in energy than the C-Ac-H center dot center dot center dot N hydrogen-bonded structure, which is the global minimum. Energy decomposition analysis indicates that the electrostatics and dispersion interactions favour the formation of C-Ac-H center dot center dot center dot N and Lp center dot center dot center dot pi complexes, respectively. Interestingly the C-Ac-H center dot center dot center dot N hydrogen-bonded complex of 2,6-difluorophenylacetylene-triethylamine showed a smaller shift in the acetylenic C-H stretching frequency than the 2,6-difluorophenylacetylene-trimethylamine complex. The observed fragmentation of the binary complexes of 2,6-difluorophenylacetylene with the four amines following resonant two-photon ionization can be explained on the basis of the intermolecular coulombic decay process.

1 aMondal, Sohidul, Islam1 aDey, Arghya1 aSen, Saumik1 aPatwari, Naresh1 aGhosh, Debashree uhttps://library.ncl.res.in/content/spectroscopic-and-ab-initio-investigation-26-difluorophenylacetylene-amine-complexes-002024nas a2200157 4500008004100000022001400041245005900055210005900114260011000173300001400283490000700297520143800304100002301742700002101765856008001786 2016 eng d a1463-907600aEffect of sequence on the ionization of guanine in DNA0 aEffect of sequence on the ionization of guanine in DNA aTHOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLANDbROYAL SOC CHEMISTRYcMAR a6526-65330 v183 a

The accurate estimation of the ionization energies and understanding the nature of the ionized states of the nucleic acid bases (NABs) are crucial to the understanding of the DNA damage mechanism. The vertical ionization energy (VIE) of guanine is the lowest among the NABs and the ionization energies are strongly affected by the environment, such as solvation and characteristics of nearby NABs. Therefore, we investigate the sequence dependence of the VIEs of guanine in B-DNA. We use the equation of motion coupled cluster method for the estimation of ionization potential with single and double excitations (EOM-IP-CCSD) and density functional theory with dispersion corrected omega B97x-D for the estimation of VIEs. A significant amount of non-additivity or cooperativity, directly proportional to charge delocalization, is noticed in the change in VIE due to the interaction with the nearby NABs. While the change in VIE due to base pairing originates predominantly from charge-dipole interactions, stacking between base pairs is a more complicated balance of dispersion and charge-dipole interactions as well as stabilization due to the delocalization of the positive charge. The long range interactions are however dominated by 1/r(3) distance dependence which shows the major role played by charge-dipole interactions. The extent of localization of positive holes on guanine is also estimated for various sequences.

1 aChakraborty, Rahul1 aGhosh, Debashree uhttps://library.ncl.res.in/content/effect-sequence-ionization-guanine-dna-001848nas a2200169 4500008004100000022001400041245012200055210006900177260007100246300001400317490000800331520115300339100001601492700002301508700002101531856012601552 2016 eng d a1520-610600aEffect of solvation on electron detachment and excitation energies of a green fluorescent protein chromophore variant0 aEffect of solvation on electron detachment and excitation energi a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcMAY a4410-44200 v1203 a

Hybrid quantum mechanics/molecular mechanics (QM/MM) is applied to the fluorinated green fluorescent protein (GFP) chromophore (DFHBDI) in its deprotonated form to understand the solvatochromic shifts in its vertical detachment energy (VDE) and vertical excitation energy (VEE). This variant of the GFP chromophore becomes fluorescent in an RNA environment and has a wide range of applications in biomedical and biochemical fields. From microsolvation studies, we benchmark (with respect to full QM) the accuracy of our QM/MM calculations with effective fragment potential (EFP) as the MM method of choice. We show that while the solvatochromic shift in the VEE is minimal (0.1 eV blue shift) and its polarization component is only 0.03 eV, the effect of the solvent on the VDE is quite large (3.85 eV). We also show by accurate calculations on the solvatochromic shift of the VDE that polarization accounts for similar to 0.23 eV and therefore cannot be neglected. The effect of the counterions on the VDE of the deprotonated chromophore in solvation is studied in detail, and a charge-smearing scheme is suggested for charged chromophores.

1 aBose, Samik1 aChakrabarty, Suman1 aGhosh, Debashree uhttps://library.ncl.res.in/content/effect-solvation-electron-detachment-and-excitation-energies-green-fluorescent-protein01595nas a2200229 4500008004100000022001400041245012500055210006900180260011000249300001400359490000600373520067500379100002501054700001901079700002101098700002101119700002101140700002301161700002601184700002401210856013101234 2016 eng d a2050-752600aEffects of the benzoxazole group on green fluorescent protein chromophore crystal structure and solid state photophysics0 aEffects of the benzoxazole group on green fluorescent protein ch aTHOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLANDbROYAL SOC CHEMISTRYcDEC a2793-28010 v43 a

Four benzoxazole-substituted GFP chromophores that differ by the length of their alkyl chain (from C1 to C12) were synthesized. In solution, the four compounds showed identical spectroscopic behavior, emitting blue light with moderate quantum yield. In the solid state, the butyl, pentyl and dodecyl derivatives strongly emitted orange light, while the methyl derivative was only weakly emissive. Based on the X-ray data and DFT calculations, emission in the solid state was explained by the formation of excimers. A very unusual ``hot-dog''-type excimer was found for the dodecyl derivative, in which two overlapping chromophores are separated by an alkyl chain.

1 aGhodbane, Abdelhamid1 aFellows, Brett1 aBright, John, R.1 aGhosh, Debashree1 aSaffon, Nathalie1 aTolbert, Laren, M.1 aFery-Forgues, Suzanne1 aSolntsev, Kyril, M. uhttps://library.ncl.res.in/content/effects-benzoxazole-group-green-fluorescent-protein-chromophore-crystal-structure-and-solid02796nas a2200229 4500008004100000022001400041245007500055210006900130260007100199300001400270490000800284520199800292100003102290700001902321700002102340700002102361700001802382700001602400700002102416700002902437856010002466 2016 eng d a1520-610600aExtension of the effective fragment potential method to macromolecules0 aExtension of the effective fragment potential method to macromol a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcJUL a6562-65740 v1203 a

The effective fragment potential (EFP) approach, which can be described as a nonempirical polarizable force field, affords an accurate first-principles treatment of noncovalent interactions in extended systems. EFP can also describe the effect of the environment on the electronic properties (e.g., electronic excitation energies and ionization and electron-attachment energies) of a subsystem via the QM/EFP (quantum mechanics/EFP) polarizable embedding scheme. The original formulation of the method assumes that the system can be separated, without breaking covalent bonds, into closed-shell fragments, such as solvent and solute molecules. Here, we present an extension of the EFP method to macromolecules (mEFP). Several schemes for breaking a large molecule into small fragments described by EFP are presented and benchmarked. We focus on the electronic properties of molecules embedded into a protein environment and consider ionization, electron-attachment, and excitation energies (single-point calculations only). The model systems include chromophores of green and red fluorescent proteins surrounded by several nearby amino acid residues and phenolate bound to the T4 lysozyme. All mEFP schemes show robust performance and accurately reproduce the reference full QM calculations. For further applications of mEFP, we recommend either the scheme in which the peptide is cut along the C-alpha-C bond, giving rise to one fragment per amino acid, or the scheme with two cuts per amino acid, along the C-alpha-C and C-alpha-N bonds. While using these fragmentation schemes, the errors in solvatochromic shifts in electronic energy differences (excitation, ionization, electron detachment, or electron-attachment) do not exceed 0.1 eV. The largest error of QM/mEFP against QM/EFP (no fragmentation of the EFP part) is 0.06 eV (in most cases, the errors are 0.01-0.02 eV). The errors in the QM/molecular mechanics calculations with standard point charges can be as large as 0.3 eV.

1 aGurunathan, Pradeep, Kumar1 aAcharya, Atanu1 aGhosh, Debashree1 aKosenkov, Dmytro1 aKaliman, Ilya1 aShao, Yihan1 aKrylov, Anna, I.1 aSlipchenko, Lyudmila, V. uhttps://library.ncl.res.in/content/extension-effective-fragment-potential-method-macromolecules00547nas a2200133 4500008004100000022001400041245010200055210006900157260000900226490000800235100002200243700002100265856012700286 2016 eng d a0065-772700aTheoretical study of the ground and excited state tautomersim in curcumin using DFT based methods0 aTheoretical study of the ground and excited state tautomersim in cAUG 0 v2521 aGrewal, Baljinder1 aGhosh, Debashree uhttps://library.ncl.res.in/content/theoretical-study-ground-and-excited-state-tautomersim-curcumin-using-dft-based-methods02118nas a2200169 4500008004100000022001400041245008200055210006900137260000800206300001400214490000800228520154800236100001601784700002301800700002101823856010401844 2017 eng d a1520-610600aElectrostatic origin of the red solvatochromic shift of DFHBDI in RNA spinach0 aElectrostatic origin of the red solvatochromic shift of DFHBDI i cMAY a4790-47980 v1213 a

Interactions with the environment tune the spectral properties of biological chromophores, e.g., fluorescent proteins. Understanding the relative contribution of the various types of noncovalent interactions in the spectral shifts can provide rational design principles toward developing new fluorescent probes. In this work, we investigate the origin of the red shift in the absorption spectra of the difluoro hydroxybenzylidene dimethyl imidazolinone (DFHBDI) chromophore in RNA spinach as compared to the aqueous solution. We systematically decompose the effects of various components of interactions, namely, stacking, hydrogen bonding, and long-range electrostatics, in order to elucidate the relative role of these interactions in the observed spectral behavior. We find that the absorption peak of DFHBDI is red-shifted by similar to 0.35 eV in RNA relative to the aqueous solution. Earlier proposals from Huang and co-workers have implicated the stacking interactions between DFHBDI and nucleic acid bases to be the driving force behind the observed red shift. In contrast, our findings reveal that the long-range electrostatic interactions between DFHBDI and negatively charged RNA. make the most significant contribution. Moreover, we notice that the opposing electrostatic fields due to the RNA backbone and the polarized water molecules around the RNA give rise to the resultant red shift. Our results emphasize the effect of strong heterogeneity in the various environmental factors that might be competing with each other.

1 aBose, Samik1 aChakrabarty, Suman1 aGhosh, Debashree uhttps://library.ncl.res.in/content/electrostatic-origin-red-solvatochromic-shift-dfhbdi-rna-spinach01748nas a2200133 4500008004100000245015000041210006900191260000800260300001200268490000800280520117900288100002101467856012601488 2017 eng d00aHybrid equation-of-motion coupled-cluster/effective fragment potential method: a route toward understanding photoprocesses in the condensed phase0 aHybrid equationofmotion coupledclustereffective fragment potenti cDEC a741-7520 v1213 a

The prediction of accurate solvatochromic shifts to the electronic excited states of chromophores is a challenge, especially in the complex biological phase, due to the importance of long-range electrostatic interactions. Hybrid quantum mechanical/molecular mechanical (QM/MM) methods are generally employed for the calculation of quantum mechanical properties in complex systems. To be predictive, there is need for an accurate quantum mechanical method that can depict the charge transfer states correctly and incorporate higher than single excited determinants in its linear response ansatz. On the contrary, for the correct depiction of the environment interactions (MM region), one needs to account for polarizability in a balanced manner. These two challenges are successfully addressed by the recently developed hybrid quantum mechanical/effective fragment potential (QM/EFP) methods, with equation-of-motion coupled-cluster (EOM-CC) as the QM method of choice. The result is an efficient method to estimate excitation energy, ionization energy, electron affinity, and redox potential in the condensed phase. It has further been extended to biological systems.

1 aGhosh, Debashree uhttps://library.ncl.res.in/content/hybrid-equation-motion-coupled-clustereffective-fragment-potential-method-route-toward01565nas a2200145 4500008004100000245011300041210006900154260000800223300001400231490000700245520100700252100001601259700002101275856012301296 2017 eng d00aInteraction energy driven biased sampling technique: a faster route to ionization spectra in condensed phase0 aInteraction energy driven biased sampling technique a faster rou cOCT a2248-22570 v383 aWe introduce a computationally efficient approach for calculating spectroscopic properties, such as ionization energies (IEs) in the condensed phase. Discrete quantum mechanical/molecular mechanical (QM/MM) approaches for spectroscopic properties in a dynamic system, such as aqueous solution, need a large sample space to obtain converged estimates, especially for the cases where particle (electron) number is not conserved, such as IEs or electron affinities (EAs). We devise a biased sampling technique based on an approximate estimate of interaction energy between the solute and solvent, that accelerates the convergence and therefore, reduces the computational cost significantly. The approximate interaction energy also provides a good measure of the spectral width of the chromophores in the condensed phase. This technique has been tested and benchmarked for (i) phenol, (ii) HBDI anion (hydroxybenzylidene dimethyl imidazolinone), and (iii) thymine in water. (c) 2017 Wiley Periodicals, Inc.1 aBose, Samik1 aGhosh, Debashree uhttps://library.ncl.res.in/content/interaction-energy-driven-biased-sampling-technique-faster-route-ionization-spectra01488nas a2200133 4500008004100000245011400041210006900155260000800224300001400232490000900246520095000255100002101205856012801226 2017 eng d00aMultiscale modelling: hybrid quantum mechanics/molecular mechanics as an example and some recent developments0 aMultiscale modelling hybrid quantum mechanicsmolecular mechanics cAPR a1455-14620 v112 3 aMost of the physical phenomena are multiscale in nature and therefore, to depict it properly one requires multiscale modelling techniques, i.e. physical models that are accurate over multiple length and time scales. The seminal work by Warshel and Levitt marks the beginning of hybrid quantum mechanics/molecular mechanics (QM/MM) method as a successful strategy towards the understanding of chemistry and physics in condensed phases and especially in biological systems. Recently, these methods have been extended to problems such as light-matter interaction, where the QM sub-system is excited from the ground to the excited states. The MM environment provides a field that changes the potential energy landscape of both the ground and excited states in a distinctly different way. In this review, we discuss the general strategy of multiscale modelling with emphasis on hybrid QM/MM and the recent developments in excited state QM/MM methods.1 aGhosh, Debashree uhttps://library.ncl.res.in/content/multiscale-modelling-hybrid-quantum-mechanicsmolecular-mechanics-example-and-some-recent02823nas a2200313 4500008004100000022001400041245009900055210006900154260000800223300001600231490000700247520186600254653001702120653001302137653001802150653001402168653003202182653001302214653001602227653001202243653001302255653001102268100002202279700002302301700001902324700002102343700001502364856013002379 2017 eng d a1463-907600aNature of selenium hydrogen bonding: gas phase spectroscopy and quantum chemistry calculations0 aNature of selenium hydrogen bonding gas phase spectroscopy and q cSEP a24179-241870 v193 a

Subsequent to the recent re-definition of hydrogen bonding by the IUPAC committee, there has been a growing search for finding the presence of this ever interesting non-covalent interaction between a hydrogen atom in an X-H group and any other atom in the periodic table. In recent gas phase experiments, it has been observed that hydrogen bonding interactions involving S and Se are of similar strength to those with an O atom. However, there is no clear explanation for the unusual strength of this interaction in the case of hydrogen bond acceptors which are not conventional electronegative atoms. In this work, we have explored the nature of Se hydrogen bonding by studying indole...dimethyl selenide (indmse) and phenol...dimethyl selenide (phdmse) complexes using gas phase IR spectroscopy and quantum chemistry calculations. We have found through various energy decomposition analysis (EDA) methods and natural bond orbital (NBO) calculations that, along with electrostatics and polarization, charge transfer interactions are important to understand Se/S hydrogen bonding and there is a delicate balance between the various interactions that plays the crucial role rather than a single component of the interaction energy. An in-depth understanding of this type of non-covalent interaction has immense significance in biology as amino acids containing S and Se are widely present in proteins and hence hydrogen bonding interactions involving S and Se atoms contribute to the folding of proteins.

 

10aCenter-Dot-O10aClusters10aCo-Ordination10aComplexes10aintermolecular interactions10aProteins10aReplacement10aspectra10aStrength10aSulfur1 aMishra, Kamal, K.1 aSingh, Santosh, K.1 aGhosh, Paulami1 aGhosh, Debashree1 aDas, Aloke uhttps://library.ncl.res.in/content/nature-selenium-hydrogen-bonding-gas-phase-spectroscopy-and-quantum-chemistry-calculations02373nas a2200301 4500008004100000022001400041245011000055210006900165260000800234490000700242520133400249653001901583653002201602653003701624653001601661653002901677653001201706653002601718653001501744653006101759100001901820700001901839700001901858700002401877700002101901700001901922856013001941 2017 eng d a1477-922600aUnprecedented solvent induced inter-conversion between monomeric and dimeric silylene-zinc iodide adducts0 aUnprecedented solvent induced interconversion between monomeric  cSEP0 v463 a

Usually, when a silylene reacts with a transition metal Lewis acid, it forms an adduct which could be either monomeric or dimeric. However, we present here that a silylene, [PhC(NtBu)(2)SiN(SiMe3)(2)] can form both monomeric [PhC(NtBu)(2)Si{N(SiMe3)(2)} -> ZnI2]center dot THF (1) and dimeric [{PhC(NtBu)(2)}(N(SiMe3)(2))SiZnI,(mu-I)](2) (2) adducts upon reaction with ZnI2. The formation of 1 and 2 relies upon the solvent used for the reaction or crystallization. When the crystallization is carried out in THF complex 1 is formed, however, when the reaction and crystallization are performed in acetonitrile complex 2 is obtained. Both 1 and 2 were structurally authenticated and the nature of the Si-Zn bond in these complexes was determined by quantum chemical calculations. In addition, a spontaneous inter-conversion between 1 and 2 just by changing the solvents has been also observed; a feature presently not known for silylene-transition metal Lewis adducts.

 

10aBis(Silylene )10aCarbene Complexes10aCrystal -structure Determination10aDative bond10aLewis acid base reaction10aLigands10aMain- group compounds10aReactivity10aSilicon(II) Bis(Trimethylsilyl)Amide; Carbonyl-Complexes1 aYadav, Sandeep1 aSangtani, Ekta1 aDhawan, Diksha1 aGonnade, Rajesh, G.1 aGhosh, Debashree1 aSen, Sakya, S. uhttps://library.ncl.res.in/content/unprecedented-solvent-induced-inter-conversion-between-monomeric-and-dimeric-silylene-zinc01825nas a2200181 4500008004100000245008000041210006900121260000800190300001600198490000700214520121800221100001601439700001901455700001801474700002101492700002101513856010901534 2018 eng d00aMachine learning prediction of interaction energies in rigid water clusters0 aMachine learning prediction of interaction energies in rigid wat cSEP a22987-229960 v203 aClassical force fields form a computationally efficient avenue for calculating the energetics of large systems. However, due to the constraints of the underlying analytical form, it is sometimes not accurate enough. Quantum mechanical (QM) methods, although accurate, are computationally prohibitive for large systems. In order to circumvent the bottle-neck of interaction energy estimation of large systems, data driven approaches based on machine learning (ML) have been employed in recent years. In most of these studies, the method of choice is artificial neural networks (ANN). In this work, we have shown an alternative ML method, support vector regression (SVR), that provides comparable accuracy with better computational efficiency. We have further used many body expansion (MBE) along with SVR to predict interaction energies in water clusters (decamers). In the case of dimer and trimer interaction energies, the root mean square errors (RMSEs) of the SVR based scheme are 0.12 kcal mol(-1) and 0.34 kcal mol(-1), respectively. We show that the SVR and MBE based scheme has a RMSE of 2.78% in the estimation of decamer interaction energy against the parent QM method in a computationally efficient way.1 aBose, Samik1 aDhawan, Diksha1 aNandi, Sutanu1 aSarkar, Ram, Rup1 aGhosh, Debashree uhttps://library.ncl.res.in/content/machine-learning-prediction-interaction-energies-rigid-water-clusters