Spatially localized molecular orbitals are of tremendous importance in the electronic structure theory as they are widely used to describe chemical bonding and speed up calculations. Nonorthogonal localized molecular orbitals (NLMOs) are known to be noticeably more localized than their conventional orthogonal counterparts. Unfortunately, the existing methods to obtain NLMOs must pre-determine and freeze the localization center of each NLMO <i>before</i> its spread is minimized. This is done to avoid the “collapse” of the occupied subspace – a problem of NLMOs becoming linearly dependent. In this presentation, we describe an unconstrained black-box method to localize nonorthogonal orbitals that determines the position of their centers automatically during the optimization process. The key to the new procedure is to construct and impose a penalty function which prevents the orbital “collapse”. An algorithm is proposed to adjust the strength of the penalty and produce the right balance between orthogonality and locality of NLMOs. The resulting method produces NLMO fast, without requiring good understanding of bonding patterns in the system (i.e. “chemical intuition”) and is demonstrated to work well a variety of molecules and materials (gamma-point only) including large systems with non-trivial bonding patterns.

Balancing act between the orthogonality and locality of one-electron orbitals

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.