Nonradiative relaxation of charge carriers at molecule-metal interfaces: Nonadiabatic molecular dynamics study

Nonadiabatic molecular dynamics simulations in combination with time-dependent Kohn-Sham density functional theory are used to study the nonradiative relaxation of charge carriers in 4-mercaptobenzonitrile (NC[sbnd]OPE1), 4-(mercaptomethyl) benzonitrile (NC-PT1), 4′-mercapto-[1,1′-biphenyl]-4-carbonitrile (NC-BP0) and 4-((4-mercaptophenyl) ethynyl) benzonitrile (NC[sbnd]OPE2) molecules absorbed on Au(111) surface. The fastest hot electron decay (∼30 fs) is obtained for the NC[sbnd]OPE1 molecule due to strong electron-phonon couplings. However, the relaxation kinetics strongly depends on the properties of the initially populated state (e.g., orbital-overlap/hybridization between the organic molecules and the substrate), on the proximity of neighboring electronic states (i.e., intraband gaps) and on the electron-phonon nonadiabatic couplings. The obtained orbital- and size-dependent relaxation dynamics is in qualitative agreement with the results of core-hole clock experiments, which indicates the possibility of modeling the interfacial electron transfer by the decay process of hot electrons.