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Core projection effects in atomic frozen‐core calculations: A numerical analysis
Author(s) -
Luaña V.,
Pueyo L.
Publication year - 1987
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.560310610
Subject(s) - valence (chemistry) , projection (relational algebra) , core electron , basis set , projector , core (optical fiber) , chemistry , atomic orbital , atomic physics , physics , electron , mathematics , quantum mechanics , computational chemistry , density functional theory , algorithm , optics
Frozen‐core calculations on the (He) 2 s 2 2 p 6 – 1 S state of the F − ion and the (Ar) 3 d 4 4 s 2 – 5 D state of the Cr atom, obtained with differently reduced basis sets and different core‐projection schemes, are presented and compared with the corresponding all‐electron results in order to analyze the behavior of the core projection under these circumstances. Severe truncation of the valence basis set can give frozen‐core results noticeably deviated from the all electron values if the regular projection (projection factors x g = 2.0) is adopted. Much better results are obtained in these cases if a softer projection ( x g = 1.0) is used for those core orbitals having high electronic density in regions where the valence basis set has low flexibility. In these circumstances the expectation value of the core projector becomes a nonvanishing correction to the valence energy because the core‐valence orthogonality is incomplete after core projection.