Quantum chemical methods of reasonable computational cost can work well for molecules in their equilibrium geometries and for molecular fragments after a bond is broken, but they are typically much less accurate in between. This is because for moderately stretched bonds the ground electronic state is poorly described by methods based on a single reference state. An interpolation method will be described that accurately models the full potential energy curve for bond breaking without the need for energy computations in the intermediate region. It does this by modeling the known mathematical structure of the solution for the electronic energy from the highly accurate, but usually impractical, full configuration interaction (FCI) method. The FCI solution describes the interaction of reference states in terms of branch points in the complex plane of the bond distance. The interpolant is a simple mathematical function constructed to model these branch points and constrained to have the known asymptotic behavior in the limits of very small and very large bond distance. In contrast to commonly used interpolation methods, which are mostly just empirical, this method is designed to describe the underlying physics. Results will be presented for hydrogen abstraction reactions.

Accurate interpolation of potential energy curves for bond breaking

256th National Meeting (2018)

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