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>Pseudoeigenvalue methods for orbital optimization. General theory and application to closed shell, open shell, and two configuration SCF wave functions
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Pseudoeigenvalue methods for orbital optimization. General theory and application to closed shell, open shell, and two configuration SCF wave functions
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机译：Pseudoeigenvalue methods for orbital optimization. General theory and application to closed shell, open shell, and two configuration SCF wave functions
A general Newtonndash;Raphson based iterative method of orbital optimization is presented. In contrast to the usual exponential transformation technique, the unitary orbital rotation matrix is specified in terms of unconstrained variables through the use of an eigenvalue equation. The method seeks improved orbitals by repeatedly constructing and diagonalizing a single symmetric matrix. The theory is applied to the closed shell, open shell, and two configuration selfhyphen;consistent field (2CSCF) wave functions. In these cases, simplifying approximations greatly reduce the computational labor without seriously impeding convergence properties. Under these approximations and a particular specification of certain parameters, the closed shell case becomes identical to the traditional Roothaan method. However, an alternative specification gives a method which has superior convergence properties to the Roothaan method. The convergence properties of the general method are examined. The general criterion for the intrinsic convergence of the method and a simple test for the stability of the converged solution are given. Also, an inexpensive enhancement based on an interpolation scheme results in accelerated and forced convergence. Some aspects of the implementation of the method are discussed. Relatively minor modifications to existing closed shell computer programs allow the calculation of open shell and 2CSCF wave functions.
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