Successes and failures of Hubbard-corrected density functional theory: The case of Mg doped LiCoO${}_2$

Abstract

We have evaluated the successes and failures of the Hubbard-corrected density functional theory (DFT+U) approach to study Mg doping of LiCoO${}_2$. We computed the effect of the U parameter on the energetic, geometric and electronic properties of two possible doping mechanisms: (1) substitution of Mg onto a Co (or Li) site with an associated impurity state and, (2) formation of impurity-state-free complexes of substitutional Mg and point defects in LiCoO${}_2$. We find that formation of impurity states results in changes on the valency of Co in LiCoO${}_2$. Variation of the Co U shifts the energy of the impurity state, resulting in energetic, geometric and electronic properties that depend significantly on the specific value of U. In contrast, the properties of the impurity-state-free complexes are insensitive to U. These results identify reasons for the strong dependence on the doping properties on the chosen value of U and for the overall difficulty of achieving agreement with the experimentally known energetic and electronic properties of doped transition metal oxides such as LiCoO${}_2$.

arXiv comment12 pages, 6 figures

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• Diffusion quantum Monte Carlo calculations of SrFeO${}_3$ and LaFeO${}_3$
• First-principles theory of doping in layered oxide electrode materials