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A guide to two‐electron integral approximations through semiorthogonal basis sets
Author(s) -
Head John D.,
Silva Susil J.
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.560360827
Subject(s) - basis (linear algebra) , scheme (mathematics) , electron , mathematics , zero (linguistics) , orthogonal basis , basis function , approximations of π , physics , quantum mechanics , mathematical analysis , geometry , linguistics , philosophy
Abstract A numerical comparison of the two‐electron integrals computed in nonorthogonal STO‐3G, semiorthogonal, and orthogonal basis sets is presented. The symmetric orthogonal basis two‐electron integrals mimic the zero differential overlap approximation but because of the nonsparse nature of S –1/2 make algorithms for integral approximations impractical. By using a semiorthogonalization scheme which orthogonalizes the weakly overlapping orbital pairs, it is shown that a systematic method for neglecting two‐electron integrals can be developed. Applications to semiempirical and nonempirical calculations are discussed.