ACCURATE ESTIMATION OF CORRELATION ENERGIES USING LOCALLY DENSE BASIS-SETS

Locally dense basis sets using the mixed 6-311G(d, p)/3-21G basis can be used to reproduce total energies and correlation energies after emp irical adjustment to 2-4 kcal/mol for a variety of small and medium si ze molecules containing hydrogen, carbon, and oxygen. Post-Hartree-Foc k methods can be calculated faster by this method by factors of 2-3, i n general, and higher in the presence of high molecular symmetry; dens ity functional approaches take longer and are impractical in the local ly dense basis set approach. It is shown that the correlation energy i n two of the better characterized density functional approaches is gen erally significantly larger than that of the post-Hartree-Fock treatme nts studied here and appears to be insensitive to the basis set employ ed. (C) 1996 by John Wiley & Sons, Inc.