Length-Gauge Optical Matrix Elements in WIEN2k

Abstract

Hybrid exchange-correlation functionals provide superior electronic structure and optical properties of semiconductors or insulators as compared to semilocal exchange-correlation potentials due to admixing a portion of the non-local exact exchange potential from a Hartree–Fock theory. Since the non-local potential does not commute with the position operator, the momentum matrix elements do not fully capture the oscillator strength, while the length-gauge velocity matrix elements do. So far, length-gauge velocity matrix elements were not accessible in the all-electron full-potential WIEN2k package. We demonstrate the feasibility of computing length-gauge matrix elements in WIEN2k for a hybrid exchange-correlation functional based on a finite difference approach. To illustrate the implementation we determined matrix elements for optical transitions between the conduction and valence bands in GaAs, GaN, (CH3NH3)PbI3 and a monolayer MoS2. The non-locality of the Hartree–Fock exact exchange potential leads to a strong enhancement of the oscillator strength as noticed recently in calculations employing pseudopotentials (Laurien and Rubel: arXiv:2111.14772 (2021)). We obtained an analytical expression for the enhancement factor for the difference in eigenvalues not captured by the kinetic energy. It is expected that these results can also be extended to other non-local potentials, e.g., a many-body GW approximation.

Investigations of the structural, mechanical and optoelectronic attributes of Rb2BB'Tl I6 ( B'= As, Ga) double perovskites for photovoltaics

“…The Wien2K software package implements the FP-LAPW method, which is a highly accurate approach for electronic structure calculations in materials science as this method provides a full-potential treatment of the electron-electron interaction within the crystal, as well as the linearized augmented plane wave basis set for representing electronic wave functions [38,39]. We carried out the computations of Rb 2 Tl I 6 ( = As, Ga) halide double perovskites using the FP-LAPW technique.…”

Physical properties of elastically and thermodynamically stable magnetic AcXO3 (X = Cr, Fe) perovskite oxides: a DFT investigation

“…The self-consistent full-potential linearized augmented plane wave approach (FP-LAPW) within the framework of ab-initio calculations [43] is used to determine the required properties of studied compounds. As the AcXO 3 (X = Cr, Fe) compounds are ferromagnetic in nature so, we have applied the spin-polarized calculations through the WIEN2K code [44]. Generalized gradient approximation (GGA) along with the modified Becke Johnson (mBJ) potential are used to evaluate the unknown exchange-correlation (XC) potential [45,46].…”

Coexistence of type-I and critical-type nodal line states in intermetallic compounds ScM (M = Cu, Ag, Au)

“…Our rst principles calculations were performed by using the Wien2k package [36], with the generalized gradient approximation (GGA) of Perdew-Burke-Ernzerhof (PBE) [37]. The expansion of the electronic wave functions was carried out by the plane-wave cutoff value of K max × R MT = 9.5 where R MT indicates the smallest atomic muf n tin sphere radius.…”