Abstract
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.
Highlights
Hydrogen absorption in many metals results in formation of metal hydrides, which were intensively studied starting from the nineteenth century [1,2,3,4,5]
We find for momentum transfers in the hexagonal basal plane almost isotropic behavior of the excitation spectra since the loss function along the 100 and 010 symmetry directions is very similar
The calculated loss function for ZrH2 is reported in Fig. 10 where one can see that the excitation spectrum in this material is dominated by a plasmon peak with an energy of 19.4 eV at small momentum transfers in all symmetry directions
Summary
Hydrogen absorption in many metals results in formation of metal hydrides, which were intensively studied starting from the nineteenth century [1,2,3,4,5]. We are not aware of optical measurements in Zr hydrides except a recent experiment [27] performed for the low-content H phases demonstrating notable variation in plasmon energies with hydrogen variation. We perform a detailed study of the collective electronic excitation spectra of Ti and Zr in the framework of time-dependent density functional theory with full inclusion of the electronic band structure. From these calculations, we obtain information on the plasmon excitations in these metals. Performing similar calculations for TiH2 and ZrH2, we investigate the impact of hydrogen absorption on the excitation spectra.
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