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A cautionary note on the use of the frozen‐core approximation for correlation energy calculations involving alkali metals
Author(s) -
Hofmann Heinz,
Hünsele Elke,
Clark Timothy
Publication year - 1990
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.540111005
Subject(s) - atomic orbital , valence (chemistry) , alkali metal , core (optical fiber) , atomic physics , gaussian , chemistry , series (stratigraphy) , molecular orbital theory , molecular orbital , computational chemistry , physics , quantum mechanics , molecule , paleontology , optics , electron , biology
Test calculations have shown that correlation energies calculated using the frozen‐core approximation in programs, such as the Gaussian series, that assume the lowest MOs to be the core orbitals may be significantly in error. Some valence orbitals in systems involving the heavier alkali metals and electronegative elements have lower energies than the highest core orbitals of the metal and are therefore erroneously omitted from the correlation energy calculation. Some examples are discussed.