Orbital-free approximations to the kinetic-energy density in exchange-correlation MGGA functionals: tests on solids

TL;DR

This paper investigates the use of orbital-free approximations to the kinetic-energy density in MGGA exchange-correlation functionals and assesses their accuracy for various solid-state properties, highlighting their potential and limitations.

Contribution

It extends previous work by evaluating the impact of deorbitalization on solid properties using different MGGA functionals, revealing property-dependent accuracy.

Findings

Orbital-free approximations can accurately predict lattice constants, bulk modulus, and cohesive energy.

Deorbitalization significantly affects band gap calculations with the mBJ MGGA potential.

The effectiveness of approximations varies depending on the specific property and functional used.

Abstract

A recent study of Mejia-Rodriguez and Trickey [Phys. Rev. A 96, 052512 (2017)] showed that the deorbitalization procedure (replacing the exact Kohn-Sham kinetic-energy density by an approximate orbital-free expression) applied to exchange-correlation functionals of the meta-generalized gradient approximation (MGGA) can lead to important changes in the results for molecular properties. For the present work, the deorbitalization of MGGA functionals is further investigated by considering various properties of solids. It is shown that depending on the MGGA, common orbital-free approximations to the kinetic-energy density can be sufficiently accurate for the lattice constant, bulk modulus, and cohesive energy. For the band gap, calculated with the modified Becke-Johnson MGGA potential, the deorbitalization has a larger impact on the results.