Starting from the Hellmann-Feynman theorem,an expression is derived for the interaction energyin forming a noncovalently bound complex.It invokes only classical electrostatics,involving thecharge distributions of the components as they are in the complex.We propose a method forobtaining these from the total charge distribution.Integration over the electronic densities is carriedout by a numerical procedure slightly modified from that of Gavezzotti.We calculate the interactionenergies for four molecular dimers at a variety of computational levels.The results are analyzed andcompared to the best estimated values available in the literature.
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