6533b7cffe1ef96bd1258462

RESEARCH PRODUCT

Computation of conical intersections by using perturbation techniques

Manuela MerchánRoland LindhLuis Serrano-andrés

subject

Potential Energy SurfacesConfiguration Interactions ; Perturbation Theory ; Potential Energy Surfaces ; Molecular Electronic States ; SCF Calculations ; Lithium Compounds ; Organic Compounds ; Wave FunctionsOrganic CompoundsChemistryComputationUNESCO::FÍSICAConfiguration InteractionsGeneral Physics and AstronomyMultireference configuration interactionConical surfaceSCF CalculationsPotential energyWave FunctionsMaxima and minima:FÍSICA [UNESCO]Molecular Electronic StatesQuantum mechanicsPerturbation TheoryLithium CompoundsStatistical physicsComplete active spacePerturbation theory (quantum mechanics)Physical and Theoretical ChemistryWave function

description

Multiconfigurational second-order perturbation theory, both in its single-state multiconfigurational second-order perturbation theory (CASPT2) and multistate (MS-CASPT2) formulations, is used to search for minima on the crossing seams between different potential energy hypersurfaces of electronic states in several molecular systems. The performance of the procedures is tested and discussed, focusing on the problem of the nonorthogonality of the single-state perturbative solutions. In different cases the obtained structures and energy differences are compared with available complete active space self-consistent field and multireference configuration interaction solutions. Calculations on different state crossings in LiF, formaldehyde, the ethene dimer, and the penta-2,4-dieniminium cation illustrate the discussions. Practical procedures to validate the CASPT2 solutions in polyatomic systems are explored, while it is shown that the application of the MS-CASPT2 procedure is not straightforward and requires a careful analysis of the stability of the results with the quality of the reference wave functions, that is, the size of the active space. Luis.Serrano@uv.es Manuela.Merchan@uv.es Roland.Lindh@teokem.lu.se

yearjournalcountryeditionlanguage
2005-01-01The Journal of Chemical Physics
https://doi.org/10.1063/1.1866096