First-Principles Calculations of Vibrational Lifetimes and Decay Channels: Hydrogen-Related Modes in Si

The vibrational lifetimes and decay channels of local vibrational modes are calculated from first principles at various temperatures. Our method can be used to predict the temperature dependence of the lifetime of any normal mode in any crystal. We focus here on the stretch modes of ${\mathrm{H}}_{2}^{*}$, ${\mathrm{H}}_{\mathrm{BC}}^{+}$, and $V\mathrm{H}\ifmmode\cdot\else\textperiodcentered\fi{}\mathrm{H}V$ in Si. The frequencies are almost identical, but the lifetimes vary from 4 to 295 ps. The calculations correctly predict the lifetimes for $T>50\text{ }\text{ }\mathrm{K}$ and illustrate the critical importance of pseudolocal modes in the decay processes of high-frequency local vibrational modes.