01710nas a2200217 4500008004100000022001400041245007900055210006900134260007300203300001000276490000800286520092600294653002901220653003001249653002201279100002201301700002701323700001601350700001801366856010801384 2012 eng d a0301-010400aExtended coupled cluster for Raman and infrared spectra of small molecules0 aExtended coupled cluster for Raman and infrared spectra of small aPO BOX 211, 1000 AE AMSTERDAM, NETHERLANDSbELSEVIER SCIENCE BVcJUL a25-320 v4033 a

In this paper we study the harmonic vibrational frequencies, infrared (IR) intensities, Raman intensities and depolarization ratio using extended coupled cluster method. Raman and IR intensities are mixed derivatives of energy with respect to the electric field and geometric perturbation whereas vibrational frequencies are derivatives of energy with respect to geometry. We use semi-numerical approach to obtain these derivatives. We have studied the effect of electron correlation and basis set for the above properties. We compare our results with non-variational coupled cluster and experimental values, wherever available. We have studied HF, BH, CH+, CO and H2CO molecules in different basis sets. For HF molecule, benchmarking is done with full CI values and basis set convergence is studied for this molecule. Effect of triples is studied for all the molecules. (C) 2012 Elsevier B.V. All rights reserved.

10aExtended coupled cluster10aIR and Raman spectroscopy10aMixed derivatives1 aJoshi, Sayali, P.1 aDutta, Achintya, Kumar1 aPal, Sourav1 aVaval, Nayana uhttp://library.ncl.res.in/content/extended-coupled-cluster-raman-and-infrared-spectra-small-molecules-001386nas a2200217 4500008004100000022001400041245009600055210006900151260009200220300001400312490000800326520050700334653003200841653001800873653004700891653002600938653002500964100002700989700002701016856012501043 2014 eng d a0026-897600aExcited state geometry optimisation using fock-space multi-reference coupled cluster method0 aExcited state geometry optimisation using fockspace multireferen a4 PARK SQUARE, MILTON PARK, ABINGDON OX14 4RN, OXON, ENGLANDbTAYLOR & FRANCIS LTDcNOV a2884-28910 v1123 a

The Fock-space multi-reference coupled cluster method is used for the geometry optimisation of the low-lying excited states of the molecules. Molecular geometries of the carbon monohydride cation (CH)(+), water (H2O), ozone (O-3) and formaldehyde (HCHO) in their low-lying excited states are optimised. Excited state gradients are calculated using finite field multi-reference coupled cluster method. We compare our results with other theoretical and/or experimental results, wherever available.

10aadiabatic excitation energy10aexcited state10aFock-space multi-reference coupled cluster10ageometry optimisation10anumerical derivative1 aDutta, Achintya, Kumar1 aBhattacharya, Sumantra uhttp://library.ncl.res.in/content/excited-state-geometry-optimisation-using-fock-space-multi-reference-coupled-cluster-002322nas a2200217 4500008004100000022001400041245007500055210006900130260006700199300001200266490000800278520158100286653001801867653002201885653001001907100002701917700002201944700001801966700001601984856010402000 2015 eng d a0020-760800aElectron attachment to DNA and RNA nucleobases: an EOMCC investigation0 aElectron attachment to DNA and RNA nucleobases an EOMCC investig a111 RIVER ST, HOBOKEN 07030-5774, NJ USAbWILEY-BLACKWELLcJUN a753-7640 v1153 a

We report a benchmark theoretical investigation of both vertical and adiabatic electron affinities of DNA and RNA nucleobases: adenine, guanine, cytosine, thymine, and uracil using equation of motion coupled cluster method. The vertical electron affinity (VEA) values of the first five states of the DNA and RNA nucleobases are computed. It is observed that the first electron attached state is energetically accessible in gas phase. Furthermore, an analysis of the natural orbitals exhibits that the first electron attached states of uracil and thymine are valence-bound in nature and undergo significant structural changes on attachment of an extra electron, which reflects in the deviation of the adiabatic electron affinity (AEA) than that of the vertical ones. Conversely, the first electron attached states of cytosine, adenine, and guanine are in the category of dipole-bound anions. Their structure, by and large, remain unaffected on attachment of an extra electron, which is evident from the observed small difference between the AEA and VEA values. VEA and AEA values of all the DNA and RNA nucleobases are found to be negative, which implies that the first electron attached states are not stable rather quasi bound. The results of all previous theoretical calculations are out of track and shows large deviation with respect to the experimentally measured values, whereas, our results are found to be in good agreement. Therefore, our computed values can be used as a reliable standard to calibrate new theoretical methods. (c) 2015 Wiley Periodicals, Inc.

10aDNA-RNA bases10aelectron affinity10aEOMCC1 aDutta, Achintya, Kumar1 aSengupta, Turbasu1 aVaval, Nayana1 aPal, Sourav uhttp://library.ncl.res.in/content/electron-attachment-dna-and-rna-nucleobases-eomcc-investigation-001652nas a2200169 4500008004100000022001400041245008500055210006900140260007100209300001400280490000700294520101700301100002701318700001801345700001601363856010301379 2015 eng d a1549-961800aEOMIP-CCSD(2)*: an efficient method for the calculation of ionization potentials0 aEOMIPCCSD2 an efficient method for the calculation of ionization a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcJUN a2461-24720 v113 a

A new approximation within the domain of EOMIP-CC method is proposed. The proposed scheme is based on the perturbative truncation of the similarity transformed effective Hamiltonian matrix. We call it the EOMIP-CCSD(2)* method, which scales as noniterative N-6 and its storage requirement is very less, compared to the conventional EOMIP-CCSD method. The existing EOMIP-CCSD(2) method has a tendency to overestimate the ionization potential (IP) values. On the other hand, our new strategy corrects for the problem of such an overestimation, which is evident from the excellent agreement achieved with the experimental values. Furthermore, not only the ionization potential but also geometry and IR frequencies of problematic double radicals are estimated correctly, and the results are comparable to the CCSD(T) method, obviously at lesser computational cost. The EOMIP-CCSD(2)* method works even for the core ionization and satellite IP, where the earlier EOMIP-CCSD(2) approximation dramatically fails.

1 aDutta, Achintya, Kumar1 aVaval, Nayana1 aPal, Sourav uhttp://library.ncl.res.in/content/eomip-ccsd2-efficient-method-calculation-ionization-potentials-101518nas a2200181 4500008004100000022001400041245007600055210006900131260007100200300001400271490000800285520085200293100001701145700002201162700002701184700001601211856010901227 2016 eng d a1089-563900aElectron detachment and subsequent structural changes of water clusters0 aElectron detachment and subsequent structural changes of water c a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcFEB a1065-10730 v1203 a

A cost-effective equation of motion coupled cluster method, EOMIP-CCSD(2), is used to investigate vertical and adiabatic ionization potential as well as ionization-induced structural changes of water clusters and compared with CCSD(T), CASPT2, and MP2 methods. The moderate N-5 scaling and low storage requirement yields EOMIP-CCSD (2) calculation feasible even for reasonably large molecules and clusters with accuracy comparable to CCSD(T) method at much cheaper computational cost. Our calculations shed light on the authenticity of EOMIP-CCSD(2) results and establish a reliable method to study of ionization energy of molecular clusters. We have further investigated the performance of several classes of DFT functionals for ionization energies of water clusters to benchmark the results and to get a reliable functionals for the same.

1 aDas, Susanta1 aSengupta, Turbasu1 aDutta, Achintya, Kumar1 aPal, Sourav uhttp://library.ncl.res.in/content/electron-detachment-and-subsequent-structural-changes-water-clusters-0