01155nas a2200169   4500008004100000022001400041245011100055210006900166260011500235300001200350490000700362520043800369100001300807700002800820700001100848856012600859       2005                        eng d  a0010-076500aElectronic spectra and ionization potentials of halogen oxides using the fock space coupled-cluster method0 aElectronic spectra and ionization potentials of halogen oxides u  aACAD SCI CZECH REPUBLIC, FLEMINGOVO NAM 2, PRAGUE 6 166 10, CZECH REPUBLICbINST ORGANIC CHEM AND BIOCHEMcJAN  a851-8630 v703 a<p>The ionization potentials and excitation energies of halogen monoxides and dihalogen oxides are studied using fully size-extensive Fock space version of multi-reference coupled-cluster theory. The low-lying excited states of ClO-, FO-, Cl2O and F2O are obtained along with the ionization spectra of Cl2O and F2O. The adiabatic electron affinity of ClO, FO and the vertical detachment energy of ClO- and FO- are also presented.</p>1 aVaval, N1 aManohar, Prashant, Uday1 aPal, S  uhttps://library.ncl.res.in/content/electronic-spectra-and-ionization-potentials-halogen-oxides-using-fock-space-coupled-001516nas a2200229   4500008004100000022001400041245011500055210006900170260007300239300001000312490000800322520066800330653002600998653002001024653001801044653002001062653001301082100002801095700001801123700001601141856012901157       2006                        eng d  a0166-128000aConstrained variational response to Fock-space multi-reference coupled-cluster theory: Some pilot applications0 aConstrained variational response to Fockspace multireference cou  aPO BOX 211, 1000 AE AMSTERDAM, NETHERLANDSbELSEVIER SCIENCE BVcAUG  a91-960 v7683 a<p>Fock space (FS) multi-reference (MR) coupled-cluster (CC) has been established to be state-of-the-art method for energies of open-shell radicals, ionized, electron attached states and excited states. Due to the multi-root nature of the method, the linear response of MRCC, however, is non-trivial. Constrained variation approach (CVA) makes it plausible to calculate response of the MRCC method efficiently. However, the approach is used for only one root of the problem at a time. In the present article, we make first implementation of the approach and present test results of dipole moments of small radicals. (c) 2006 Elsevier B.V. All rights reserved.</p>10aconstrained variation10acoupled-cluster10aDipole moment10aMulti-reference10aresponse1 aManohar, Prashant, Uday1 aVaval, Nayana1 aPal, Sourav  uhttps://library.ncl.res.in/content/constrained-variational-response-fock-space-multi-reference-coupled-cluster-theory-some-001838nas a2200253   4500008004100000020002200041022001400063245018300077210006900260260016600329300001200495490000800507520079600515653000801311653001801319653001901337653001101356653001901367100002801386700001601414700001601430700001401446856012401460       2007                        eng d  a978-0-7354-0477-9  a0094-243X00aConstrained variational response to fock-space multi-reference coupled-cluster theory: formulation for excited-state electronic structure calculations and some pilot applications0 aConstrained variational response to fockspace multireference cou  a2 Huntington Quadrangle, Ste 1no1, Melville, NY 11747-4501 USAbEuropean Soc Computat Methods Sci & Engn; Minist Natl Educ & Religious Affairs; E4 Comp EngncSEP  a337-3440 v9633 a<p>Fock-space (FS) multi-reference (MR) coupled-cluster (CC) method has emerged as compact tool to account for electronic structure of open-shell systems and molecules in low-lying excited states. Development of linear response (LR) has been one of the challenging problems in FSMRCC due to multiple-root nature of effective Hamiltonian. The recently developed constrained variational approach (CVA) has opened up a promising tool for efficient evaluation of analytic response properties. In this article, we present formulation of the method for excited state calculations. We discuss the decoupling of equations as a result of spin-adaptation and present some preliminary results for analytical dipole moments and polarizabilities of some molecules in low-lying triplet excited states.</p>10aCVA10aDipole moment10aexcited states10aFSMRCC10apolarizability1 aManohar, Prashant, Uday1 aPal, Sourav1 aMaroulis, G1 aSimos, TE  uhttps://library.ncl.res.in/content/constrained-variational-response-fock-space-multi-reference-coupled-cluster-theory-001343nas a2200157   4500008004100000022001400041245015500055210006900210260007300279300001200352490000800364520064400372100002801016700001601044856012501060       2007                        eng d  a0009-261400aDipole moments and polarizabilities of some small radicals using constrained variational response to fock-space multi-reference coupled-cluster theory0 aDipole moments and polarizabilities of some small radicals using  aPO BOX 211, 1000 AE AMSTERDAM, NETHERLANDSbELSEVIER SCIENCE BVcAPR  a321-3250 v4383 a<p>In this Letter, we present dipole moments and polarizabilities of some open-shell doublet radicals, obtained analytically using constrained variational response to Fock-space (FS) multi-reference (MR) coupled cluster (CC) theory. These radicals can be treated as electron attached (EA) states of the corresponding closed-shell cations. Additionally, we also report analytical polarizabilities of some doublet radicals, which can be considered as ionized (IP) states of the corresponding anions. We compare our results with finite field FSMRCC response and the available benchmark results. (c) 2007 Elsevier B.V. All rights reserved.</p>1 aManohar, Prashant, Uday1 aPal, Sourav  uhttps://library.ncl.res.in/content/dipole-moments-and-polarizabilities-some-small-radicals-using-constrained-variational01757nas a2200181   4500008004100000022001400041245016900055210006900224260012500293300001100418490000800429520092800437100001601365700002801381700001801409700001601427856013201443       2009                        eng d  a0021-960600aFirst- and second-order electrical properties computed at the FSMRCCSD level for excited states of closed-shell molecules using the constrained-variational approach0 aFirst and secondorder electrical properties computed at the FSMR  aCIRCULATION & FULFILLMENT DIV, 2 HUNTINGTON QUADRANGLE, STE 1 N O 1, MELVILLE, NY 11747-4501 USAbAMER INST PHYSICScJUL  a0241020 v1313 a<p>Fock space multireference coupled-cluster (FSMRCC) method emerged as an efficient tool to describe the electronic structure of nearly degenerate cases. Development of linear response has been one of the challenging problems in FSMRCC due to the multiple-root nature of the effective Hamiltonian. A response from any of the roots would span the space for getting the properties. Hence, all roots perturbed by the external field would proliferate the excited states. We recently developed the FSMRCC method for the efficient evaluation of analytic response properties using a constrained variation approach. In this paper, we present analytic dipole moments and polarizabilities of H2O, O-3, and CH+ molecules in low-lying excited states along with brief discussion of singlet triplet decoupling of (1,1) sector of FSMRCC resulting from spin adaptation. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3167796]</p>1 aBag, Arijit1 aManohar, Prashant, Uday1 aVaval, Nayana1 aPal, Sourav  uhttps://library.ncl.res.in/content/first-and-second-order-electrical-properties-computed-fsmrccsd-level-excited-states-closed-000678nas a2200169   4500008004100000245011800041210006900159260003100228300001200259490000700271100002800278700002400306700001600330700001800346700001600364856012800380       2010                        eng d00aOn some aspects of fock-space multi-reference coupled-cluster singles and doubles energies and optical properties0 asome aspects of fockspace multireference coupledcluster singles   aNetherlandsbSpringercAPR  a375-3930 v111 aManohar, Prashant, Uday1 aShamasundar, K., R.1 aBag, Arijit1 aVaval, Nayana1 aPal, Sourav  uhttps://library.ncl.res.in/content/some-aspects-fock-space-multi-reference-coupled-cluster-singles-and-doubles-energies-and01805nas a2200229   4500008004100000022001400041245011500055210006900170260007300239300001000312490000800322520095000330653001801280653002201298653002901320100002001349700002801369700001701397700001801414700001601432856012701448       2013                        eng d  a0301-010400aExtended coupled cluster through nth perturbation order for molecular response properties: a comparative study0 aExtended coupled cluster through nth perturbation order for mole  aPO BOX 211, 1000 AE AMSTERDAM, NETHERLANDSbELSEVIER SCIENCE BVcMAY  a45-510 v4173 a<p>In this paper, we have presented and analyzed the extended coupled cluster (ECC) energy functional, truncated up to nth perturbation order in which expansion is limit to operators of the single and double excitations. The expression for the first order energy derivatives based on the above truncation schemes has been derived and numerically analyzed. We have done a comparative study for dipole moment in various perturbative ECC (n) methods (2 &lt;= n &lt;= 5) for three systems (HF, H2O and BH) at equilibrium geometry. We have particularly studied two variants of ECC (4) and ECC (5*) method for stretched geometry. We have analyzed the contribution of important terms present in ECC functional based on perturbative argument. We have compared our results with standard coupled cluster (CCSD) as well as cubic truncated ECC and also benchmarked with the full CI results wherever available. (c) 2013 Elsevier B.V. All rights reserved.</p>10aDipole moment10aEnergy functional10aExtended coupled cluster1 aGupta, Jitendra1 aManohar, Prashant, Uday1 aGhosh, Aryya1 aVaval, Nayana1 aPal, Sourav  uhttps://library.ncl.res.in/content/extended-coupled-cluster-through-nth-perturbation-order-molecular-response-properties-001513nas a2200181   4500008004100000022001400041245005700055210005500112260008700167300001100254490000800265520088000273100002701153700002801180700001801208700001601226856008901242       2014                        eng d  a0021-960600aGround state of naphthyl cation: singlet or triplet?0 aGround state of naphthyl cation singlet or triplet  a1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USAbAMER INST PHYSICScMAR  a1143120 v1403 a<p>We present a benchmark theoretical investigation on the electronic structure and singlet- triplet(ST) gap of 1- and 2-naphthyl cations using the CCSD(T) method. Our calculations reveal that the ground states of both the naphthyl cations are singlet, contrary to the results obtained by DFT/B3LYP calculations reported in previous theoretical studies. However, the triplet states obtained in the two structural isomers of naphthyl cation are completely different. The triplet state in 1-naphthyl cation is (pi,sigma) type, whereas in 2-naphthyl cation it is (pi,sigma) type, The S-T gaps in naphthyl cations and the relative stability ordering of the singlet and the triplet states are highly sensitive to the basis set quality as well as level of correlation, and demand for inclusion of perturbative triples in the coupled-cluster ansatz. (c) 2014 AIP Publishing LLC.</p>1 aDutta, Achintya, Kumar1 aManohar, Prashant, Uday1 aVaval, Nayana1 aPal, Sourav  uhttps://library.ncl.res.in/content/ground-state-naphthyl-cation-singlet-or-triplet-001979nas a2200373   4500008004100000022001400041245012500055210006900180260000800249300001400257490000800271520089200279653000701171653000701178653002701185653000701212653000701219653002401226653002501250653000801275653002301283653001801306653001501324653000701339653000801346653002701354653000701381653000701388653001301395100001801408700002701426700002801453856012401481       2017                        eng d  a0974-362600aResolution of the identity and cholesky representation of EOM-MP2 approximation: implementation, accuracy and efficiency0 aResolution of the identity and cholesky representation of EOMMP2  cOCT  a1611-16260 v1293 aWe present a Resolution of Identity and Cholesky Decomposition Based Implementation of EOM-MP2 approximation. The RI and CD based EOM-MP2 shows significant speed-up and less storage requirement than the conventional canonical version and can be applied to very large systems. The new algorithm used for this implementation eliminates the most storage requiring four-index quantities resulting in the decrease of storage requirement, reduction in I/O penalties and improved parallel performance, at the expense of more floating point operations. Therefore, the speed-up compared to conventional EOM-MP2 method is more prominent in case of EA, EE and SF case where the storage bottleneck is significant than the EOM-IP-MP2 method, where the storage requirement is significantly less. However, the RI/CD based EOM-IP-MP2 can be coupled with frozen natural orbitals to gain further speed-up.10aCC10aCD10aCholesky decomposition10aEA10aEE10aelectron attachment10aelectron correlation10aEOM10aequation-of-motion10aexcited state10aionization10aIP10aMP210aResolution-of-identity10aRI10aSF10aspinflip1 aKumar, Dinesh1 aDutta, Achintya, Kumar1 aManohar, Prashant, Uday  uhttps://library.ncl.res.in/content/resolution-identity-and-cholesky-representation-eom-mp2-approximation-implementation