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Implications of unitary invariance for gradient theory
Author(s) -
Jayatilaka Dylan,
Handy Nicholas C.
Publication year - 1992
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.560420307
Subject(s) - unitary state , atomic orbital , mathematical proof , molecular orbital , molecular orbital theory , quantum mechanics , unitary transformation , physics , classical mechanics , theoretical physics , mathematics , molecule , geometry , quantum , political science , law , electron
This paper shows how the invariance of the energy to unitary rotations in the occupied orbitals and in the virtual orbitals can be used to determine some elements of the derivative molecular orbitals, which are important for gradient theory. Solution of the usual coupled‐perturbed Hartree–Fock equations for these elements is thus unnecessary, eliminating considerable effort. We also give proofs which show clearly that special conditions are required.