First-principles study of the pressure dependence of the structural and vibrational properties of the ternary metal hydrideCa2RuH6

Abstract

The influence of pressure on the structural and vibrational properties of ${\mathrm{Ca}}_{2}\mathrm{Ru}{\mathrm{H}}_{6}$ has been investigated using periodic density functional theory calculations performed at the local density approximation (LDA) and generalized gradient approximation (GGA) levels. At ambient pressure, the calculated structure and vibrational frequencies are in satisfactory agreement with experimental data. The calculated $P\text{\ensuremath{-}}V$ curves could be fitted with the Vinet equation of state, yielding ${B}_{0}=67.6$ and ${B}_{0}=58.5\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ at the LDA and GGA levels, respectively, and ${B}_{0}^{\ensuremath{'}}=4.0$ at both theoretical levels. The unit cell parameter is found to decrease faster with increasing pressure than the Ru--H bond length. The calculated pressure dependence of the vibrational frequencies agrees well with experiment for ${\ensuremath{\nu}}_{5}({T}_{2g})$ but not for ${\ensuremath{\nu}}_{9}({A}_{1g})$.