Hydrogenation-driven phase transition in single-layer TiSe.

First-principles calculations based on density-functional theory are used to investigate the effects of hydrogenation on the structural, vibrational, thermal and electronic properties of the charge density wave (CDW) phase of single-layer TiSe. It is found that hydrogenation of single-layer TiSe is possible through adsorption of a H atom on each Se site. Our total energy and phonon calculations reveal that a structural phase transition occurs from the CDW phase to the T phase upon full hydrogenation. Fully hydrogenated TiSe presents a direct gap semiconducting behavior with a band gap of 119 meV. Full hydrogenation also leads to a significant decrease in the heat capacity of single-layer TiSe.