Search results for "Many−Body Problem"

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Elementary presentation of self‐consistent intermediate Hamiltonians and proposal of two totally dressed singles and doubles configuration interactio…

1994

Intermediate Hamiltonians are effective Hamiltonians which are defined on an N‐dimensional model space but which only provide n<N exact eigenvalues and the projections of the corresponding eigenvectors onto the model space. For a single root research, the intermediate Hamiltonian may be obtained from the restriction of the Hamiltonian to the model space by an appropriate, uniquely defined dressing of the diagonal energies or of the first column. Approximate self‐consistent dressings may be proposed. The simplest perturbative form gives the same result as the original 2nd order intermediate Hamiltonian or the ‘‘shifted Bk’’ technique but it is of easier implementation. Self‐consistent inclus…

HamiltoniansHamiltonians ; Configuration Interaction ; Scf Calculations ; Eigenvalues ; Eigenvectors ; Degeneration ; Many−Body Problem ; Electronic StructureDiagonalGeneral Physics and AstronomyElectronic structureMany−Body ProblemMany-body problemsymbols.namesakePauli exclusion principleQuantum mechanicsPhysical and Theoretical Chemistry:FÍSICA::Química física [UNESCO]Eigenvalues and eigenvectorsMathematical physicsMathematicsDegenerate energy levelsEigenvaluesScf CalculationsConfiguration interactionUNESCO::FÍSICA::Química físicaConfiguration InteractionElectronic StructureDegenerationsymbolsEigenvectorsHamiltonian (quantum mechanics)The Journal of Chemical Physics
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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
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