Communication: Density functional theory embedding with the orthogonality constrained basis set expansion procedure.

Content Provider	Europe PMC
Author	Culpitt, Tanner Brorsen, Kurt R. Hammes-Schiffer, Sharon
Copyright Year	2017
Description	Density functional theory (DFT) embedding approaches have generated considerable interest in the field of computational chemistry because they enable calculations on larger systems by treating subsystems at different levels of theory. To circumvent the calculation of the non-additive kinetic potential, various projector methods have been developed to ensure the orthogonality of molecular orbitals between subsystems. Herein the orthogonality constrained basis set expansion (OCBSE) procedure is implemented to enforce this subsystem orbital orthogonality without requiring a level shifting parameter. This scheme is a simple alternative to existing parameter-free projector-based schemes, such as the Huzinaga equation. The main advantage of the OCBSE procedure is that excellent convergence behavior is attained for DFT-in-DFT embedding without freezing any of the subsystem densities. For the three chemical systems studied, the level of accuracy is comparable to or higher than that obtained with the Huzinaga scheme with frozen subsystem densities. Allowing both the high-level and low-level DFT densities to respond to each other during DFT-in-DFT embedding calculations provides more flexibility and renders this approach more generally applicable to chemical systems. It could also be useful for future extensions to embedding approaches combining wavefunction theories and DFT.
Abstract	Density functional theory (DFT) embedding approaches have generated considerable interestin the field of computational chemistry because they enable calculations on larger systemsby treating subsystems at different levels of theory. To circumvent the calculation of thenon-additive kinetic potential, various projector methods have been developed to ensurethe orthogonality of molecular orbitals between subsystems. Herein the orthogonalityconstrained basisset expansion (OCBSE) procedure is implemented to enforce this subsystemorbital orthogonality without requiring a level shifting parameter. This scheme is asimple alternative to existing parameter-free projector-based schemes, such as theHuzinaga equation. The main advantage of the OCBSE procedure is that excellent convergencebehavior is attained for DFT-in-DFT embedding without freezing any of the subsystemdensities. For the three chemical systems studied, the level of accuracy is comparable toor higher than that obtained with the Huzinaga scheme with frozen subsystem densities.Allowing both the high-level and low-level DFT densities to respond to each other duringDFT-in-DFT embedding calculations provides more flexibility and renders this approach moregenerally applicable to chemical systems. It could also be useful for future extensions toembedding approaches combining wavefunction theories and DFT.
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Page Count	4
ISSN	00219606
Volume Number	146
DOI	10.1063/1.4984777
PubMed Central reference number	PMC5648574
Issue Number	21
PubMed reference number	28576084
Journal	The Journal of Chemical Physics [J Chem Phys]
e-ISSN	10897690
Language	English
Publisher	AIP Publishing LLC
Publisher Date	2017-06-01
Access Restriction	Open
Rights License	Published by AIP Publishing. Copyright © 2017 Author(s)
Content Type	Text
Resource Type	Article
Subject	Physics and Astronomy Medicine Physical and Theoretical Chemistry