Revisiting the configurations of hydrogen impurities in SrTiO3: Insights from first-principles local vibration mode calculations

The specific configurations of hydrogen impurities in SrTiO3 (STO) are still ambiguous. In this study, we systematically investigate the configurations and vibrational properties of hy-drogen impurities in cubic STO using first-principles local vibration mode calculations. Em-ploying the appropriate hybrid exchange correlation functional with the fraction of exact ex-change setting to 0.2, we revisit the interstitial hydrogen (Hi), Hi complexes (2Hi), and various intrinsic cation vacancy complexes with Hi, including VSr-Hi, VSr-2Hi, VTi-Hi, and VTi-2Hi. Comparison of the computed vibrational frequencies with experimental infrared absorption bands reveals that Hi, with a frequency of 3277 cm-1, is unlikely to account for the dominant absorption bands near 3500 cm-1. Instead, strontium vacancy complexes with interstitial hydro-gen (VSr-Hi and VSr-2Hi) exhibit vibrational frequencies that align with the main absorption bands, whereas titanium vacancy complex with two interstitial hydrogen (VTi-2Hi) corresponds to additional absorption bands around 3300 cm-1. These findings provide insights into the im-portance of hydrogen-related complexes in governing the electronic properties of STO, and meanwhile underscore the necessity of employing accurate exchange correlation functionals for reliable theoretical predictions of vibrational properties.