Implementation of atomic basis set composed of 1s Gaussian and 1s Slater-type orbitals to carry out quantum mechanics molecular calculations

A mixed atomic basis set formed with Is Slater-type orbitals and Is floatin g spherical Gaussian orbitals is implemented. Evaluation of multicenter int egrals is carried out using a method based on expansion of binary products of atomic basis functions in terms of a complete basis set, and a systemati c analysis is performed. The proposed algorithm is very stable and furnishe s fairly good results for total energy and geometry. An LCAO-SCF test calcu lation is carried out on LiH. The trends observed show that there are some combinations of mixed orbitals that are appropriate to describe the system. (C) 1999 John Wiley & Sons, Inc.