Hydrogen exhibits qualitatively different charge states depending on the host material, as nicely explained by the state-of-the-art impurity-state calculation. Motivated by a recent experiment [Nature 546, 124 (2017)], we show that the complex oxide SrCoO2.5 represents an interesting example, in which the interstitial H appears as a deep-level center according to the commonly-used transition level calculation, but no bound electron can be found around the impurity. Via a combination of charge difference analysis, density of states projection and constraint magnetization calculation, it turns out that the H-doped electron is spontaneously trapped by a nonunique Co ion and is fully spin-polarized by the onsite Hund's rule coupling. Consequently, the doped system remains insulating, whereas the antiferromagnetic exchange is slightly perturbed locally.
@article{arxiv.1805.11766,
title = {The role of interstitial hydrogen in SrCoO$_{2.5}$ antiferromagnetic insulator},
author = {Li Liang and Shuang Qiao and Shunhong Zhang and Jian Wu and Zheng Liu},
journal= {arXiv preprint arXiv:1805.11766},
year = {2018}
}