Projection-based embedding offers a simple framework for embedding wavefunction theories in density functional theory. Underlying this embedding is a heuristic for translating the chemically-intuitive idea of a set of embedded atoms into a set of embedded orbitals on which the embedded wavefunction calculation will be performed. For single-point calculations, a successful heuristic has been to first localize the occupied Kohn-Sham orbitals, and then assign these localized orbitals to the embedded region based on atomic population analysis. However, during a large geometry change – such as a chemical reaction – the nature of the localized orbitals, as well as their atomic populations can change dramatically. This can lead to qualitatively different embedded orbitals between geometries, resulting in unphysical cusps and even discontinuities in the potential energy surface. In this talk, we present an even-handed framework for localized orbital partitioning that ensures that the span of the embedded orbitals is invariant throughout a geometry coordinate. We illustrate this problem and solution with a simple example of an SN<sub>2</sub> reaction. We then apply our method to a nitrogen umbrella flip in a cobalt-based CO2 reduction catalyst and to the binding of CO to a Cu(111) surface.

Even-handed active space selection in projection-based wavefunction-in-DFT embedding

255th National Meeting (2018)

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