Please use this identifier to cite or link to this item: http://hdl.handle.net/2248/5002
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dc.contributor.authorChaudhuri, R. K-
dc.contributor.authorChattopadhyay, S-
dc.contributor.authorMahapatra, U. S-
dc.contributor.authorFreed, K. F-
dc.date.accessioned2010-02-09T13:32:32Z-
dc.date.available2010-02-09T13:32:32Z-
dc.date.issued2010-01-
dc.identifier.citationJournal of Chemical Physics, Vol. 132, No. 3, pp. 034105-1 - 034105-18en
dc.identifier.issn0021 - 9606-
dc.identifier.urihttp://hdl.handle.net/2248/5002-
dc.description.abstractThe improved virtual orbital-complete active space configuration interaction (IVO-CASCI) method is extended to determine the geometry and vibrational frequencies for ground and excited electronic states using an analytical total energy gradient scheme involving both first and second order analytical derivatives. Illustrative applications consider the ground state geometries of the benzene (C6H6), biphenyl (C12H10), and alanine dipeptide (CH3CONHCHCH3CONHCH3) molecules. In addition, the IVO-CASCI geometry optimization has been performed for the first excited singlet (1B2u) and triplet states (3B1u) of benzene to assess its applicability for excited and open-shell systems. The D6h symmetry benzene triplet optimization produces a saddle point, and a descent along the unstable mode produces the stable minimum. Comparisons with Hartree-Fock, second order Möller-Plesset perturbation theory, complete active space self-consistent field (CASSCF), and density functional theory demonstrate that the IVO-CASCI approach generally fares comparable to or better for all systems studied. The vibrational frequencies of the benzene and biphenyl molecules computed with the analytical gradient based IVO-CASCI method agree with the experiment and with other accurate theoretical estimates. Satisfactory agreement between our results, other benchmark calculations, and available experiment demonstrates the efficacy and potential of the method. The close similarity between CASSCF and IVO-CASCI optimized geometries and the greater computational efficiency of the IVO-CASCI method suggests the replacement of CASSCF treatments by the IVO-CASCI approach, which is free from the convergence problems that often plague CASSCF treatments.en
dc.language.isoenen
dc.publisherAmerican Institute of Physicsen
dc.relation.urihttp://dx.doi.org/10.1063/1.3290203en
dc.rights© American Institute of Physicsen
dc.subjectDensity Functional Theoryen
dc.subjectGradient Methodsen
dc.subjectGround Statesen
dc.subjectHF Calculationsen
dc.subjectOrbital Calculationsen
dc.subjectOrganic Compoundsen
dc.subjectPerturbation Theoryen
dc.subjectSCF Calculationsen
dc.subjectTotal Energyen
dc.subjectTriplet Stateen
dc.subjectVibrational Statesen
dc.subjectSelf-Consistent-Field Methodsen
dc.subjectDensity-Functional Theoryen
dc.subjectPerturbation Theoryen
dc.subjectPotential Energy Surfacesen
dc.subjectExcited Electronic Statesen
dc.titleMolecular applications of analytical gradient approach for the improved virtual orbital-complete active space configuration interaction methoden
dc.typeArticleen
Appears in Collections:IIAP Publications



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