Numerical comparison of generalized surface hopping, classical analog, and selfconsistent eikonal approximations for nonadiabatic scattering A selfconsistent eikonal treatment of diabatic rearrangement: Model H++H2 calculationsa)We develop an eikonal treatment of electronic transitions in many-atom collisions, in which classical nuclear trajectories are self-consistently coupled to quantal electronic transitions. The treatment starts with a discussion of the electronic representations required to assure that Hamiltonian matrices are Hermitian. The amplitudes of wave functions are found to satisfy coupled equations which are expanded in powers of a local de Broglie wavelength. Time-dependent equations are transformed to derive a Hamiltonian formalism that couples nuclear positions and momenta with electronic amplitUdes. Cross sections are obtained from flux conservation and also from T-matrix elements.(3) 7138

Charge transfer photoinduced by steady light absorption on a silicon surface leads to formation of a surface photovoltage (SPV). The dependence of this voltage on the structure of surface adsorbates and on the wavelength of light is studied with a combination of ab initio electronic structure calculations and the reduced density matrix for the open excited system. Our derivations provide time averages of surface electric dipoles, which follow from a time-dependent density matrix (TDDM) treatment using a steady state solution for the TDDM equations of motion. Ab initio calculations have been carried out in a basis set of Kohn-Sham orbitals obtained by a density functional treatment using atomic pseudopotentials. Applications have been done to a H-terminated Si(111) surface and for adsorbed Ag, with surface coverage ranging from 0 to 3/24 of a monolayer. Calculations done also for amorphous Si agree with measured values of the SPV versus incident photon frequency for H-terminated a-Si. Surface adsorbates are found to enhance light absorption and facilitate electronic charge transfer at the surface. Specifically, Ag clusters add electronic states in the energy gap area, provide stronger absorption in the IR and visible spectral regions, and open up additional pathways for surface charge transfer. Our treatment can be implemented for a wide class of photoelectronic materials relevant to solar energy capture.

Relaxation pathways of photoinduced electronic redistribution at nanostructured semiconductor surfaces are obtained from time-dependent density matrix and ab initio electronic structure methods, giving electronic changes in energy and space over time. They are applied to a Ag cluster on a Si(111) surface, initially photoexcited by a short pulse, and show that the Ag cluster adds surface-localized states that enhance electron transfer. Results on the time evolution of population density distributions in energy and in space, for valence and conduction bands, explore the energy band landscape of a Si slab, with various relaxation pathways ending up in a charge-separated state, with a hole in the Si slab and an electron in the adsorbed Ag cluster. Calculated electronic relaxation times for Si(111)/H are of the same order as experimental values for similar semiconductor systems.