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Speaker: Brian Busemeyer, CCQ
Title: New applications of AFQMC to realistic defect problems via an embedding approach
Abstract:
Defects are fundamental elements of material design, useful for introducing charge or magnetism, as well as engineering color centers and qubit realizations. In many systems, characterizing defects experimentally is challenging, while first-principles methods must languish in large supercells in order to model isolated defects. If, on top of this, the defect requires delicate treatment of electron correlation, the problem may seem impossible, because correlated methods tend to be computationally demanding even in smaller primitive cells. In this QMC Meeting, I introduce a new approach to handling just such a scenario: embedded first-principles AFQMC for defects. Correlations within a given radius around the defect are treated with AFQMC, and this calculation is embedded in a bulk treated with independent-electron theory. I'll demonstrate this approach on two defects within hexagonal boron nitride, and demonstrate that both accurate treatment of correlations and the bulk environment are critical. In these cases, we found that favorable scaling of AFQMC allowed us to expand the radius defining the correlated orbitals until all quantities were well-converged. This approach opens new possibilities for accurate many-body treatment of defect systems using embedding in combination with AFQMC. Additionally, abundant connections with the extensive literature on embedding methods suggest methodological expansions of this approach may be able to tackle a wide variety of problems.