Photoconductivities from band states and a dissipative electron dynamics: Si(111) without and with adsorbed Ag clusters

Abstract

A new general computational procedure is presented to obtain photoconductivities starting from atomic structures, combining ab initio electronic energy band states with populations from density matrix theory, and implemented for a specific set of materials based on Si crystalline slabs and their nanostructured surfaces without and with adsorbed Ag clusters. The procedure accounts for charge mobility in semiconductors in photoexcited states, and specifically electron and hole photomobilities at Si(111) surfaces with and without adsorbed Ag clusters using ab initio energy bands and orbitals generated from a generalized gradient functional, however with excited energy levels modified to provide correct bandgaps. Photoexcited state populations for each band and carrier type were generated using steady state solution of a reduced density matrix which includes dissipative medium effects. The present calculations provide photoexcited electronic populations and photoinduced mobilities resulting from applied electric fields and obtained from the change of driven electron energies with their electronic momentum. Extensive results for Si slabs with 8 layers, without and with adsorbed Ag clusters, show that the metal adsorbates lead to substantial increases in the photomobility and photoconductivity of electrons and holes.

Photofragmentation of Tetranitromethane: Spin-Unrestricted Time-Dependent Excited-State Molecular Dynamics

“…The computational description of photoinduced reactions is a great challenge and a practical demand. Reduced density matrix (RDM) equation of motion allows analysis of photoinduced relaxation of charge carriers for semiconductors. − Nonadiabatic molecular dynamics (NAMD) has been used to study photophysical processes, such as charge transfer, and photochemical processes, such as photoisomerization and photodissociation, due to nonadiabatic dynamics. ,− The photoluminescence yields of silicon nanocrystals have been investigated through NAMD with a multireference treatment of the electronic structure . In a recent study, spin-restricted time-dependent excited-state molecule dynamics (TDESMD) was used to simulate the photofragmentation of neutral lanthanide cyclopentadienyl complexes, where the computed fragments show good agreement with fragments experimentally observed by photoionization time-of-flight (PI-TOF) mass spectrometry. − It should be noted that TDESMD is interpreted as “molecular dynamics for time-dependent electronic configuration”.…”

Photoabsorbance of supported metal clusters: ab initio density matrix and model studies of large Ag clusters on Si surfaces

“…However, our experience from extensive photoconductivity calculations for these slab systems is that energy bands are flat and k -point averages involve minor changes in the intensity of light absorption. 55…”

“…However, our experience from extensive photoconductivity calculations for these slab systems is that energy bands are flat and k-point averages involve minor changes in the intensity of light absorption. 55 Spin-polarized calculations (not included here) with separate electronic densities for up and down spins of open-shell adsorbates have been done with HSE06 for Ag 33 Si 240 H 52 . They show a difference in the band gaps calculated for up and down spins, but they are of the same magnitude as the band gap without spin polarization.…”