Free vibrational relaxation of H adsorbed on a Si(1 0 0) surface investigated with the multi-configurational time-dependent Hartree method

The results of a quantum-mechanical study of vibrational relaxation of hydrogen adsorbed on a Si(1 0 0) surface with the multi-configurational time-dependent Hartree (MCTDH) method are presented. A two-dimensional subsystem is coupled non-linearly to a bath of harmonic oscillators (phonons of the Si bulk), and the relaxation of subsystem vibrations proceeds primarily via a two-phonon process. Characteristic times of the system evolution agree well with our previous perturbation theory study. The vibrational population decay is non-exponential, exhibiting pronounced recurrences due to finite bath size. The dependence of the lifetimes of the vibrational levels on the bath size and on the coupling details is investigated.