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An MC‐SCF procedure using an orthogonal transformation represented by a direct sum of two‐by‐two rotations
Author(s) -
Igawa Akira
Publication year - 1985
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.560280204
Subject(s) - atomic orbital , transformation (genetics) , molecular orbital , rotation (mathematics) , chemistry , computational chemistry , permutation (music) , ground state , convergence (economics) , physics , electron , molecular physics , mathematics , quantum mechanics , molecule , geometry , biochemistry , acoustics , economics , gene , economic growth
N molecular orbitals are transformed to K (≦ N ) molecular orbitals, which are appropriate for an orbital optimization by two‐by‐two orthogonal rotations among themselves. This transformation is determined by using the second‐order structure of the variational energy surface. The optimum K /2 rotation angles are exactly determined. This helps to ensure the reliability of convergence. K /2 two‐by‐two rotations are repeated among these K transformed orbitals. Then, two‐electron molecular integrals are calculated by transformations among only 16 elements and by a permutation among K 4 /8 elements. Calculational time is considerably reduced compared with that of more usual transformations. Test calculations have been carried out on the ground state of CO . It shows that this procedure brings the calculation to the local region rapidly and reliably.