Exact density functional and wave function embedding schemes based on orbital localization

Abstract

Articles you may be interested in (2014)] is proposed. We also use localized orbitals to partition the system, but instead of augmenting the Fock operator with a somewhat arbitrary level-shift projector we solve the Huzinaga-equation, which strictly enforces the Pauli exclusion principle. Second, the embedding of WFT methods in local correlation approaches is studied. Since the latter methods split up the system into local domains, very simple embedding theories can be defined if the domains of the active subsystem and the environment are treated at a different level. The considered embedding schemes are benchmarked for reaction energies and compared to quantum mechanics (QM)/molecular mechanics (MM) and vacuum embedding. We conclude that for DFT-in-DFT embedding, the Huzinaga-equation-based scheme is more efficient than the other approaches, but QM/MM or even simple vacuum embedding is still competitive in particular cases. Concerning the embedding of wave function methods, the clear winner is the embedding of WFT into low-level local correlation approaches, and WFT-in-DFT embedding can only be more advantageous if a non-hybrid density functional is employed. Published by AIP Publishing.[http://dx

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

“…1-14 Recent embedding methods have focused on ensuring the orthogonality of subsystem orbitals through a variety of projector methods, 8,[11][12][13] avoiding the need to calculate the non-additive kinetic potential 1,2,15-19 that appears in DFT-in-DFT embedding. While some of these projector methods require a level shifting parameter, 8 others are parameter free.…”

“…While some of these projector methods require a level shifting parameter, 8 others are parameter free. [11][12][13] One recent chemical application of a parameter-free approach 12 uses a self-consistent field (SCF) version of the Huzinaga equation 20 to enforce subsystem orbital orthogonality. In this implementation, however, the density of the environment needed to be frozen during the SCF procedure to ensure numerical stability and reasonable convergence behavior.…”

“…In this implementation, however, the density of the environment needed to be frozen during the SCF procedure to ensure numerical stability and reasonable convergence behavior. 12 Herein we present the orthogonality constrained basis set expansion 21,22 (OCBSE) procedure as a simple alternative to the Huzinaga equation for enforcing orbital orthogonality in the context of density embedding. Previously we used the OCBSE procedure in embedding theory for multicomponent DFT, 23 where electrons and specified protons are treated quantum mechanically on the same level, but herein this approach is applied to conventional electronic DFT.…”

“…10, except for the bond length of OH , which is 0.978 Å as given in Ref. 12. These test systems are depicted in Fig.…”

“…To enable direct comparison, the threshold for orbital inclusion was chosen to ensure that the number of orbitals included in the active subsystem was the same as that reported in Ref. 12. The remaining occupied orbitals were assigned to subsystem B.…”