Explicitly correlated SCF study of small hydrides

摘要

The "soft Coulomb hole" method of Chakravorty and Clementi has been implemented in a Gaussian lobe-orbital (GLO) program to include explicit electron-electron correlation in molecules according to a modified form of Coulomb's law in a program for workstations and personal computers (PCLOBE): f(R-12) = (1 - exp(-w(R-12)(2)))/R-12, w = scaling parameter. Twice as many two-electron integrals must be calculated compared to the usual Hartree-Fock-Roothaan algorithm, but this "correlated self-consistent field (SCF)" method may be embedded within well-known SCF computer codes and yields more than 90% of the correlation energy in run times less than twice that of the restricted Hartree-Fock (RHF) method. A two-parameter model of correlation is calibrated on I-IF and LiH using the 6-311G** basis as Gaussian lobe orbitals. The quantum Monte Carlo energies of LiH and HF were fitted to within 150 cal/mol, but the scaling model for first-row atoms is less good for H-2. This work shows promise as a fast way to modify the Hartree-Fock-Roothaan method for accuracy approaching quantum Monte Carlo methods. This proof-of-concept work offers extension to modeling solvation properties of water solutions in high-pressure liquid chromatography (HPLC). (C) 2001 John Wiley & Sons, Inc. [References: 31]