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A reassessment of some restricted Hartree–Fock limit molecular energies and an investigation of the applicability of Ermler and Kern's procedure for their estimation
Author(s) -
George Philip,
Trachtman Mendel,
Bock Charles W.
Publication year - 1981
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.540020314
Subject(s) - diatomic molecule , polyatomic ion , chemistry , molecule , basis set , gaussian , basis (linear algebra) , computational chemistry , hartree–fock method , limit (mathematics) , atomic physics , physics , mathematics , mathematical analysis , geometry , organic chemistry
Abstract New estimates of Hartree–Fock limit energies ( E RHF ) for selected AH and AH n hydrides, diatomic and linear polyatomic molecules have been made utilizing E SCF values recently reported in the literature for HF, N 2 , CO, NH 3 , and CH 4 which are very close to the respective limits. These new values have been used to investigate the applicability of Ermler and Kern's procedure for estimating E RHF : i.e., a factor f is first evaluated from data for reference molecules, where f = E RHF / E SCF , which is then used with E SCF values for other molecules to obtain their E RHF values. f has been evaluated for three groups of reference moleculesHF, H 2 O, NH 3 , CH 4 , N 2 , and CO; CH 4 , C 2 H 2 , C 2 H 4 , and C 2 H 6 ; and C 2 H 2 , HCN, and N 2 utilizing E SCF data in the literature for many Gaussian‐type orbital (GTO) basis sets together with some new values calculated at the (9,5,1) to (13,8,2) levels. Trends in the variation of f within each group of reference molecules from one basis set to another, and the trends in f from one group of reference molecules to another, are discussed in detail. To minimize the influence of these effects in an E RHF estimate it is recommended that the f value should be derived from reference molecules which possess a similar combination of structural features, i.e., bonded hydrogen, single, double, or triple bonds, and the number of lone‐pair electrons. Further calculations show that an f value based on data for closed‐shell molecules is not applicable to open‐shell species.