Validation of density functionals for transition metals and intermetallics using data from quantitative electron diffraction

TL;DR

This study validates various density functional theory (DFT) approximations against experimentally measured structure factors from electron diffraction for transition metals and intermetallics, highlighting the performance differences among functionals.

Contribution

It provides a comprehensive comparison of DFT functionals against experimental data for transition metals and intermetallics, and suggests using low-order structure factors to tune the U parameter in LDA+U.

Findings

PW91 and EV93 GGA functionals best match experimental data for metals

LDA+U with carefully chosen U achieves excellent agreement across systems

Experimental Fg can be used to tune U in LDA+U calculations

Abstract

Accurate low-order structure factors (Fg) measured by quantitative convergent beam electron diffraction (QCBED) were used for validation of different density functional theory (DFT) approximations. 23 low-order Fg were measured by QCBED for the transition metals Cr, Fe, Co, Ni, and Cu, and the transition metal based intermetallic phases {\gamma}-TiAl, {\beta}-NiAl and {\gamma}1-FePd using a multi-beam off-zone axis (MBOZA) method and then compared with Fg calculated ab-initio by DFT using the local spin density approximation (LDA) and LDA+U, and different generalized gradient approximations (GGA) functionals. Different functionals perform very differently for different materials and crystal structures. Among the GGA functionals, PW91 and EV93 achieve the best overall agreement with the experimentally determined low-order Fg for the five metals, while PW91 performs the best for the three intermetallics. The LDA+U approach, through careful selection of U, achieves excellent matches with the experimentally measured Fg for all the metallic systems investigated in this paper. Similar to the band gap for semiconductors, it is proposed that experimentally determined low-order Fg can be used to tune the U term in LDA+U method DFT calculations for metals and intermetallics.