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Convergence optimization of restricted open-shell self-consistent field calculations

✍ Scribed by Christian Kollmar

Publisher: John Wiley and Sons
Year: 1997
Tongue: English
Weight: 263 KB
Volume: 62
Category: Article
ISSN: 0020-7608
DOI: 10.1002/(sici)1097-461x(1997)62:6<617::aid-qua5>3.0.co;2-z

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✦ Synopsis

Different self-consistent field SCF iteration schemes for open-shell systems are discussed. After a brief summary of the well-known level shifting and Ž . damping procedure, we describe the quadratically convergent SCF QCSCF approach based on the gradient and the Hessian matrix in a space of orbital rotation parameters. An analytical expression for the latter is derived for the general many-shell case. Starting from the expression for the energy change obtained by the QCSCF method, we then present a simplified direct procedure avoiding matrix diagonalization but also the difficulties of the QCSCF method in handling the Hessian matrix. Numerical calculations on some open-shell systems involving transition-metal complexes show that this method leads to rapid and reliable convergence of the iteration process in cases where the usual SCF procedure of iterative diagonalization tends to diverge.

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