Search results for "Self−Consistent Field"

showing 2 items of 2 documents

General occurrence of polar twisted minima in the ionic singlet excited surfaces of polyenes

1982

Except for a few cases, the lowest closed shell SCF solutions for the twisted geometries of polyenes involves delocalized nonpolarized MO’s, and represents a meaningless mixture of radicalar gound state and ionic excited states. Higher (quasi) solutions allow a realistic approach of the polarized ionic states. Orthogonality to the radicalar ground state may be imposed without important loss of energy. Further extensive CI does not modify significantly the situation. These statements are illustrated through ab initio calculations of butadiene and hexatriene. This approach allows us to show that slight distortions stablize polar minima even in ’’homosymmetric’’ molecules such as all‐trans hex…

ChemistryUNESCO::FÍSICAGeneral Physics and AstronomyIonic bondingElectronic structurePolyenesExcited StatesSelf−Consistent FieldDelocalized electronElectronic StructureAb initio quantum chemistry methods:FÍSICA [UNESCO]Polyenes ; Self−Consistent Field ; Electronic Structure ; Excited StatesExcited statePhysics::Atomic and Molecular ClustersSinglet statePhysical and Theoretical ChemistryAtomic physicsPhysics::Chemical PhysicsGround stateOpen shell
researchProduct

Self‐consistent intermediate Hamiltonians : A coupled cluster type formulation of the singles and doubles configuration interaction matrix dressing

1995

This paper presents a new self‐consistent dressing of a singles and doubles configuration interaction matrix which insures size‐consistency, separability into closed‐shell subsystems if localized molecular orbitals (MOs) are used, and which includes all fourth order corrections. This method yields, among several schemes, a reformulation of the coupled cluster method, including fully the cluster operators of single and double excitations, and partially those of the triples (Bartlett’s algorithm named CCSDT‐1a). Further improvement can be easily included by adding exclusion principle violating corrections. Since it leads to a matrix diagonalization, the method behaves correctly in case of nea…

PhysicsHamiltoniansDiagonalizable matrixGeneral Physics and AstronomyLocalized molecular orbitalsConfiguration interactionMany−Body ProblemUNESCO::FÍSICA::Química físicaMany-body problemSelf−Consistent FieldConfiguration Interactionsymbols.namesakeMatrix (mathematics)Pauli exclusion principleCoupled clusterHamiltonians ; Self−Consistent Field ; Many−Body Problem ; Perturbation Theory ; Configuration Interaction ; AlgorithmsQuantum mechanicssymbolsPerturbation TheoryPerturbation theory (quantum mechanics)Physical and Theoretical Chemistry:FÍSICA::Química física [UNESCO]Algorithms
researchProduct