Two‐center molecular repulsion integrals over slater functions

For the general two‐electron two‐center integral over Slater functions, use of the Neumann expansion for the electron‐electron interaction term yields the standard auxiliary functions. These are expanded and integrated explicitly by two independent methods. The resulting simple analytic formula for the total integral is completely general, requiring only the Slater function quantum numbers and exponents and the internuclear separation. Hence all two‐electron hydrid, coulomb, exchange, and one‐center integrals are considered. The efficiency of calculation of this expression is compared with those of other methods, indicating an order of magnitude improvement in speed over recursion for the exchange integral.