Generic implementation of semi-analytical CI gradients for NDDO-type methods |
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Authors: | S Patchkovskii A Koslowski W Thiel |
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Institution: | (1) Steacie Institute for Molecular Sciences, National Research Council of Canada, 100 Sussex Drive, Ottawa, ON, Canada, K1A 0R6;(2) Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim, Germany |
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Abstract: | Generic semi-analytical energy gradients are derived and implemented for NDDO-type methods, by using numerical integral and
Fock matrix derivatives in the context of an otherwise analytical approach for configuration interaction (CI) and other non-variational
treatments. The correctness, numerical precision, and performance of this hybrid approach are established through comparisons
with fully numerical and fully analytical calculations. The semi-analytical evaluation of the CI gradient is generally much
faster than the fully numerical computation, but somewhat slower than a fully analytical calculation, which however shows
the same scaling behavior. It is the method of choice whenever a fully analytical CI gradient is not available due to the
lack of analytical integral derivatives. The implementation is generic in the sense that it can easily be extended to any
new NDDO-type Hamiltonian. The present development of a semi-analytical CI gradient will facilitate studies of electronically
excited states with recently proposed NDDO methods that include orthogonalization corrections.
Dedicated to Professor Karl Jug on the occasion of his 65th birthday |
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