Self-consistent embedding theory for locally correlated configuration interaction wave functions in condensed matter

Abstract

We present new developments on a density-based embedding strategy for the electronic structure of localized feature in periodic, metallic systems [see T. Kluner et al., J. Chem. Phys. 116, 42 (2002), and references therein]. The total system is decomposed into an embedded cluster and a background, where the background density is regarded as fixed. Its effect on the embedded cluster is modeled as a one-electron potential derived from density functional theory. We first discuss details on the evaluation of the various contributions to the embedding potential and provide a strategy to incorporate the use of ultrasoft pseudopotentials in a consistent fashion. The embedding potential is obtained self-consistently with respect to both the total and embedded cluster densities in the embedding region, within the framework of a frozen background density. A strategy for accomplishing this self-consistency in a numerically stable manner is presented. Finally, we demonstrate how dynamical correlation effects can be treated within this embedding framework via the multireference singles and doubles configuration interaction method. Two applications of the embedding theory are presented. The first example considers a Cu dimer embedded in the (111) surface of Cu, where we explore the effects of different models for the kinetic energy potential. We find that the embedded Cu density is reasonably well-described using simple models for the kinetic energy. The second, more challenging example involves the adsorption of Co on the (111) surface of Cu, which has been probed experimentally with scanning tunneling microscopy [H. C. Manoharan et al., Nature (London) 403, 512 (2000)]. In contrast to Kohn-Sham density functional theory, our embedding approach predicts the correct spin-compensated ground state.

Accurate basis set truncation for wavefunction embedding

“…Among these are the QM/MM, [1][2][3][4][5][6] ONIOM, 7,8 fragment molecular orbital (FMO), [9][10][11][12][13][14][15] and wavefunction theory (WFT)-in-density functional theory (DFT) embedding [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] approaches, which allow for the treatment of systems that would not be practical using conventional WFT approaches. In particular, WFT-in-DFT embedding utilizes the theoretical framework of DFT embedding to enable the WFT description of a given subsystem in the effective potential that is created by the remaining electronic density of the system.…”

Understanding cross‐boundary events in ONIOM QM:QM' calculations

“…To achieve high accuracy, an expensive correlated wavefunction calculation can be embedded in the environment of a relatively fast DFT or wavefunction method. 10,11 For large systems an alternative is the combination of a density functional as QM method with a semiempirical method or density-functional tight-binding (DFTB) as QM' method. [12][13][14] The flexibility of the ONIOM QM:QM' scheme makes it possible to choose an optimum combination of QM and QM' for a wide range of different phenomena.…”

Calculation of nuclear magnetic resonance shieldings using frozen-density embedding

“…25 The FDE scheme has also been applied to free energy calculations in solution and biological environments. 26,27 Furthermore, Iannuzzi et al have made use of FDE for molecular dynamics simulations, 28 and the same embedding potential as in FDE was employed by Carter and co-workers, [29][30][31][32][33][34] in an "ab initio in DFT" embedding approach combining a wave-function-based treatment of an atom or molecule absorbed on a surface with a periodic DFT description of the surface.…”