DMRG on top of plane-wave Kohn-Sham orbitals: case study of defected boron nitride

Abstract

In this paper, we analyze the numerical aspects of the inherently multi-reference density matrix renormalization group (DMRG) calculations on top of the periodic Kohn-Sham density functional theory (DFT) using the complete active space (CAS) approach. Following the technical outline related to the computation of the Hamiltonian matrix elements and to the construction of the active space, we illustrate the potential of the framework by studying the vertical many-body energy spectrum of hexagonal boron nitride (hBN) nano-flakes embedding a single boron vacancy point defect with prominent multi-reference character. We investigate the consistency of the DMRG energy spectrum from the perspective of sample size, basis size, and active space selection protocol. Results obtained from standard quantum chemical atom-centered basis calculations and plane-wave based counterparts show excellent agreement. Furthermore, we also discuss the spectrum of the periodic sheet which is in good agreement with extrapolated data of finite clusters. These results pave the way toward applying DMRG method in extended correlated solid state systems, such as point qubit in wide band gap semiconductors.

Hybridized defects in solid-state materials as artificial molecules

“…We choose a real-space as opposed to a periodic density functional approach to avoid artificial interactions across neighboring supercells which could obscure the defect-defect interactions of interest. Furthermore, it has been shown that realspace electronic structure calculations on hexagonal boron nitride (hBN) nanoflakes can be extrapolated onto periodic calculations [46,47]. The size of the nanoflake, around 220 atoms in total, is chosen such that there are at least 4 unit cells of hBN beyond the boundaries of the localized defect orbitals before termination with passivating hydrogen atoms.…”

Defect polaritons from first principles

“…The subscripted letters in the names of the defect systems are the atoms of the hBN nanoflake that are being replaced, and their substituents CH, C, and V correspond to a carbon atom bonded to a hydrogen atom, a carbon atom, and a vacancy, respectively. To theoretically model the electronic structure of these defect systems, we use the pseudopotential, real-space density functional theory method Octopus [72][73][74], as it has been shown that real-space electronic structure calculations on hexagonal boron nitride (hBN) nanoflakes can be extrapolated onto periodic calculations [75,76]. For the ground state, we use the Perdew, Burke, and Ernzerhof (PBE) generalized gradient approximation exchange-correlation functional [77], and for the excited state calculation, we use a functional based on the local density approximation (LDA) [78,79].…”