An accurate numerical multicenter integration for molecular orbital theory

A powerful and accurate numerical three-dimensional integration scheme was developed especially for molecular orbital calculations. A multicenter inte gral is decomposed into the sum of single-center integrals using nuclear we ight functions and calculated using Gaussian quadrature rules. The decompos ed single-center integrands show strong anisotropy. With a careful selectio n of the Gaussian quadrature rule according to the anisotropy, it is possib le to obtain an accuracy of 13 digits with a small number of integration po ints for the overlap integrals, normalization integrals, and molecular inte grals for the hydrogen molecule. (C) 1999 John Wiley & Sons, Inc.