The two faces of static correlation | Zendy

Joshua W. Hollett | Zendy; Peter M. W. Gill | Zendy

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The two faces of static correlation

Author(s) -

Joshua W. Hollett,

Peter M. W. Gill

Publication year - 2011

Publication title -

the journal of chemical physics

Language(s) - English

Resource type - Journals

SCImago Journal Rank - 1.071

H-Index - 357

eISSN - 1089-7690

pISSN - 0021-9606

DOI - 10.1063/1.3570574

Subject(s) - degeneracy (biology) , physics , instability , beryllium , wave function , basis (linear algebra) , type (biology) , charge (physics) , quantum mechanics , function (biology) , basis set , quantum electrodynamics , atomic physics , mathematical physics , molecule , mathematics , nuclear physics , geometry , ecology , bioinformatics , biology , evolutionary biology

Restricted Hartree-Fock (RHF) and UHF wavefunctions for beryllium-like ions with nuclear charge 3 ≤ Z ≤ 5 are found using a near-complete Slater basis set. The triplet (RHF → UHF) instability and correlation energy are investigated as a function of Z and we find that the instability vanishes for Z > 4.5. We reproduce this surprising behavior using a minimal-basis model and, by comparing with the stretched H(2) molecule, conclude that "static" (also known as nondynamical, near-degeneracy, first-order, or strong) correlation comes in two flavors: one that can be captured by UHF and another that cannot. In the former (Type A), there is an "absolute near-degeneracy"; in the latter (Type B), there is a "relative near-degeneracy." This dichotomy clarifies discussions of static correlation effects.

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