Rigorous use of symmetry within the construction of multidimensional potential energy surfaces.

Abstract

A method is presented, which allows for the rigorous use of symmetry within the construction of multidimensional potential energy surfaces (PESs). This approach is based on a crude but very fast energy estimate, which retains the symmetry of a molecule. This enables the efficient use of coordinate systems, which mix molecular and permutational symmetry, as, for example, in the case of normal coordinates with subsets of localized normal coordinates. The impact of symmetry within the individual terms of an expansion of the PES is studied together with a symmetry consideration within the individual electronic structure calculations. A trade between symmetry within the surface and the electronic structure calculations has been observed and has been investigated in dependence on different coordinate systems. Differences occur between molecules belonging to Abelian point groups in contrast to non-Abelian groups, in which further benefits can be achieved by rotating normal coordinates belonging to degenerate vibrational frequencies. In general, the exploitation of surface symmetry was found to be very important within the construction of PESs of small and medium-sized molecules-irrespective of the coordinate system. Benchmark calculations are provided for formaldehyde, ethene, chloromethane, and cubane.