First-principles density-functional calculations on HCr₃O₈: An exercise to better understand the ACr₃O₈(A = alkali metal) family

Abstract

Accurate ab initio density-functional calculations are performed to understand structural stability, electronic structure, and magnetic properties of the ACr₃O₈(A = H, Li, Na, K, Rb, Cs) series. The ground-state structures for the compounds with A = Li−Rb take the same KCr₃O₈-type atomic arrangement (space group C2/m), whereas CsCr₃O₈adopts a modified atomic architecture (prototype; space group Pnma), in agreement with available experimental findings. The hypothetical compound HCr₃O₈is found to stabilize in an LiV₃O₈-type structure (space group P2₁/m), with an unexpectedly large equilibrium volume. The electronic structures of the ACr₃O₈compounds are analyzed using density-of-states, charge-density, and electron-localization-function plots, and all are found to exhibit semiconducting (insulating at 0 K) properties with very narrow band gaps. The Cr atoms occur in two different valence states and all compounds (except NaCr₃O₈) are found to exhibit antiferromagnetic ordering of magnetic moments at 0 K.