CALCULATION OF 2-CENTER INTEGRALS BETWEEN SLATER-TYPE ORBITALS

Two-center overlap, nuclear-attraction and kinetic energy integrals between Slater-type orbitals (STOs) centered on two different points are calculated. The expansion of STO in terms of spherical harmonics centered on an atom displaced from the first one is used. Coefficients of the expansion are stored in an adjustable array (its size depends on quantum numbers of the STO involved) in the first step of the calculation. In the second step a simple and closed formula is used for obtaining the required type of integral between STOs (with quantum numbers in the range for which calculations in the first step have been performed).