Role of Exchange and Correlation in Predicting Structures and Properties of Fluoride Materials

The study of fluorine-based inorganic compounds has captured the attention of condensed matter physicists as a route to engineer novel states of matter. Here, we present a density functional theory (DFT) study on fluorides with structures ranging from simple to complex, including KF (rock salt), MnF$_2$ and VF$_2$ (rutile), KMnF$_3$ (perovskite), and Na$_3$MnF$_6$ and Na$_6$ScF$_6$ (cryolite). % The focus is on understanding the accuracy of various exchange-correlation functionals for the prediction of structural, electronic, and phonon properties at four different levels of theory, i.e., the local density approximation (LDA), generalized gradient approximation (GGA), meta-GGA, and hybrid functional level with exact exchange. % Specifically, we draw attention to the meta-GGA functional MS2 [Sun \emph{et al}, Phys.\ Rev.\ Lett., \textbf{111}, 106401 (2013)], demonstrating that although it shows improvements over the LDA and GGA functionals in predicting structural properties of fluorides, %,\emph{i.e.} volume errors $\leq2\%$, MS2 generally performs poorer for the electronic and phonon properties. % Our study provides useful insights for predictive design of functional halide compounds using computational models based on DFT.