Computational quantum chemistry in terms of multicenter Slater-type orbitals: Entirely numerical procedure for the accurate evaluation of the basic integrals

Ab initio quantum mechanical calculations in terms of multicenter Slater‐type orbitals require accurate evaluation of basic one‐ and two‐electron integrals, a difficult mathematical task that becomes in particular challenging in the two‐electron case as four different expansion centers are involved. Here, we propose to illustrate the feasibility of attacking the problem of the multiple integrations needed entirely by numerical quadratures, in conjunction with a strategic program organization that allows evaluating simultaneously sets of thousands of integrals exploiting the mean characteristics of the integrands. This approach, envisaged and implemented many years ago by two of the present authors (C.G., O.S.), perhaps without adequate exposure, is endowed in our experience with good properties. The program package, which allows dealing on the same footing with linear and nonlinear molecular geometries, has been largely revised by introducing suitable adjustments and improvements (in particular extension to orbitals with azimuthal quantum number l = 3). © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003