Three‐dimensional numerical integration for electronic structure calculations

Abstract Two three‐dimensional numerical schemes are presented for molecular integrands such as matrix alements of one‐electron operators occuring in the Fock operator and expectation values of one‐electron operators describing molecular properties. The schemes are based on a judicious partitioning of space so that product‐Gauss integration rules can be used in each region. Convergence with the number of integration points is such that very high accuracy (8–10 digits) may be obtained with obtained with a modest number of points. The use of point group symmetry to reduce the required number of points is discussed. Examples are given for overlap, nuclear potential, and electric field gradient integrals.