01516nas 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-001805nas 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-0