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Interaction energies between closed‐shell systems: The correlation energy in the random phase approximation
Author(s) -
Szabo Attila,
Ostlund Neil S.
Publication year - 2009
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560120846
Subject(s) - random phase approximation , open shell , electronic correlation , degenerate energy levels , hartree–fock method , unitary state , quantum mechanics , invariant (physics) , physics , atomic orbital , perturbation theory (quantum mechanics) , dispersion (optics) , quantum electrodynamics , electron , political science , law
A new expression for the correlation energy of closed‐shell systems is presented. This correlation energy, obtained from the random phase approximation, is size consistent, invariant to unitary transformations of degenerate orbitals, and has the important property that at long range it yields the coupled Hartree‐Fock dispersion force between interacting systems. Since ordinary second‐order many‐body perturbation theory, when applied to the same problem, gives uncoupled Hartree‐Fock dispersion forces, calculations based on our formula, which still requires only particle‐hole two‐electron integrals, are expected to lead to significantly improved potential energy curves.