NONEMPIRICAL WAVE-FUNCTIONS FOR VERY LARGE MOLECULES .3. EXTENSION OFTHE PRDDO M AND PRDDO/M/FCP METHOD TO MAIN-ROW ELEMENTS GA-BR/

We describe the extension of the modified version of the method of par tial retention of diatomic differential overlap (PRDDO/M) and its froz en-core potential implementation (PRDDO/M/FCP) to third main row eleme nts. New minimal basis sets containing contracted double-zeta represen tations of the 3d shell and single-zeta representations for the 1s, 2s p, 3sp, and 4sp shells have been developed for Ga-Br. These basis sets yield molecular geometries which are in much better agreement with ex periment than are traditional STO-3G representations. The frozen-core potential version replaces the explicit treatment of the 1s, 2sp, and 3spd core orbitals with a pseudopotential which is based on the actual core-valence integrals. PRDDO/M calculations are at least one order o f magnitude faster than are ab initio calculations with similar basis sets and provide molecular geometries and atomic charges which are in good agreement with the reference ab initio calculations. (C) 1997 Joh n Wiley & Sons, Inc.