Automatic Generation of Intermolecular Potential Energy Surfaces.

A method is developed for automatic generation of intermolecular two-body, rigid-monomer potential energy surfaces based on symmetry-adapted perturbation theory (SAPT). It is also possible to substitute SAPT interaction energies by values computed using sufficiently high-level supermolecular methods. The long-range component of the potential is obtained from a rigorous asymptotic expansion with ab initio computed coefficients which seamlessly connects to SAPT interaction energies at large separations. An accompanying software package has been developed and tested successfully on eight systems ranging in size from the Cl-HO dimer to the cyclotrimethylene trinitramine dimer containing 42 atoms total. The potentials have a typical fit error of about 0.2 kcal/mol in the negative energy region. The accuracy may be further improved by including off-atomic sites or increasing their number. All aspects of potential development were designed to work reliably on a broad range of systems with no human intervention.