Approximate interaction energy in terms of overlap integral

摘要

When the natural orbital expansion is applied to the total wave function, the (electronic) kinetic energyTis exactly expressible in terms of the overlap integralSbetween the natural orbitals. Then we can derive an implicit but rigorous relation between the total energyEand the overlap integral based on the integral form of the virial theorem. For a particular case of two interacting atoms with a large internuclear separation, an approximate but explicit relation is obtained betweenEandS, and its implication is discussed. An illustrative example is given for the H+2system.