Collective electronic excitations in Ti and Zr and their dihydrides

Electron excitation spectra in Ti and Zr transition metals are calculated in the framework of time-dependent density functional theory. Several peaks found in the obtained loss functions are interpreted as collective excitations. The energy positions of the dominating bulk plasmons are in close agreement with the energy loss experiments. We investigated how the absorption of hydrogen modifies the dielectric properties of these materials. It is shown that the main plasmon energy blueshifts in a such process, again in agreement with experimental observations. On base of the calculated bulk dielectric functions of all these systems, we performed analysis of the excitation spectra at surfaces and nanoparticles. Several plasmon peaks in these systems with rather short lifetimes are found at reduced energies. It is shown how the nanoparticle excitation spectra are modified in the ultraviolet-frequency range upon hydrogen absorption.
The research was funded by the Tomsk Polytechnic University Competitiveness Enhancement Program. I.V.S. acknowledges financial support from the Ministry of Education and Science of the Russian Federation within the governmental program Megagrants (State Task No. 3.9003.2017/220 or 3.9003.2017/9.10). V.M.S. and E.V.C. acknowledge the partial support from the University of the Basque Country UPV/EHU, Grant No. IT-756-13 and the Spanish Ministry of Economy, Industry and Competitiveness MINEICO, Project Nos. FIS2016-76617-P and FIS2016-75862-P. V.M.S. acknowledges project PI2017-30 of the Departamento de Educación, Política Lingüística y Cultura of the Basque government.