Fourth-order Møller–Plesset perturbation theory (MP4) is formulated for localized internal orbitals of closed-shell systems. Unlike previous localized perturbation theories, our formulation is strictly identical with canonical MP4 theory if no further approximations are made. In the local... mehr

Computational results are reported which demonstrate the performance of the local correlation method, including convergence behavior and supercomputer timing. Calculations at the local MP4(SDQ) level with the 6-311G** basis have been carried out for molecules as big as octatetraene, demonstrating... mehr

Using redundant inverse-power distance coordinates we present a series of optimizations on randomly generated argon clusters containing 12, 24, and 48 argon atoms. Our results clearly show that inverse distance coordinates perform significantly better for optimizing the geometries of atomic... mehr

Using the scaled quantum-mechanical (SQM) force field approach with direct scaling of individual primitive force constants, we derive optimal scaling factors by a least-squares fit to the experimentally observed fundamentals of some selected “simple” fluorocarbons. We use the derived scaling... mehr

Copyright: Copyright © 1998 John Wiley & Sons, Inc. mehr

A simple way of generating starting orbitals for multiconfigurational SCF calculations (particularly of the CAS type) is to use the natural orbitals of the unrestricted Hartree–Fock wave function. Significant fractional occupancy of a UHF natural orbital indicates that the orbital should be... mehr

The direct inversion in the iterative subspace (DIIS) method is applied to several simple SCF wave functions in an effective Fock matrix formulation. The following cases are treated: high-spin-restricted open shell, open-shell singlet, and two-configuration wave functions. Open-shell singlet... mehr