Multicentre two-electron Coulomb and exchange integrals over Slater functions evaluated using a generalized algorithm based on nonlinear transformations

When calculating molecular electronic energies, the contributions involving the Coulomb operator for bielectronic terms are required rapidly and to high chemically significant accuracy. The atomic orbital basis functions chosen in the present work are Slater-type functions (STFs). These functions can be expressed as finite linear combinations of B functions which are suitable to apply the Fourier-transform method. The difficulties of the numerical evaluation of the analytic expressions of the integrals of interest arise mainly from the presence of two- or three-dimensional integral representations. In this work, we present a generalized algorithm for a precise and fast numerical evaluation of molecular integrals over STFs. Numerical results obtained with C2H2, C2H4 and CH4 molecules show the efficiency of the approach presented in this work. Comparisons with the existing codes are also listed.