Projection-based quantum embedding is a formally exact density functional theory embedding that, when implemented with an appropriate post-Hartree Fock method, can correctly account for the electron correlation of a chosen moiety of a more extensive system. The choice of partitioning the embedded subspace in this method is not trivial, and there have been many proposed partitioning methods involving localized orbitals. However, using a singular value decomposition (SVD) to guide the partitioning of the embedded subspace has been shown to be a robust way to ensure the invariance of the chosen subspace against orbital deformation while capturing the local correlation energy. Additionally, using SVD to truncate the virtual subspace is a cost conscience way of prioritizing those virtual orbitals that most contribute to the correlation energy in the chosen active space. To date, SVD partitioning of the embedded subspace has been successfully demonstrated for closed-shell systems. Here we present an extension of the SVD-informed subsystem projected atomic orbital decomposition partitioning method to open-shell systems. This open-shell method is built on restricted open-shell mean-field orbitals that ensure the fidelity of the subsystem spin, a necessary condition of a well-defined embedding method. Furthermore, the same formalism is naturally extended to an SVD-informed concentric localization and subsequent truncation of the virtual space. In this talk, we will describe projection-based quantum embedding and SVD-based partitioning of the active space, provide example test cases for this proposed open-shell embedding, and discuss the limits of this extension in open-shelled systems.

Active space partitioning for open-shelled systems in projection-based quantum embedding

Where thousands of chemistry professionals meet to share ideas and advance scientific and technical knowledge. Spring 2023 abstracts, posters, and presentations will launch at the end of March.

ACS Spring 2023

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