Direct evaluation of the Pauli repulsion energy using `classicalʹ wavefunctions in hybrid quantum/classical potential energy surfaces

A new procedure for evaluating the Pauli repulsion energy in hybrid quantum/classical treatments is discussed and applied to two model systems: the hydrogen-bonded water dimer and the charged system H2O/Li+. The Pauli repulsion is evaluated by associating temporary wavefunctions with the classical region and then exploiting the equivalence of Pauli exclusion and permutational antisymmetry. The proposed hybrid quantum/classical treatment is devoid of any empirical parameters. Comparison with full quantum mechanical calculations suggests that the method may be applied to a wide variety of systems.