We treat electronic dynamics at surfaces of nanostructured semiconductors induced by absorption of visible light using reduced density matrices and properties obtained from ab initio electronic structure calculations, to focus on two non-adiabatic phenomena: (a) how active electrons interacting non-adiabatically with atoms at the surface undergo electronic transitions and (b) how active electrons interacting by exchanging energy with excitons in the medium undergo a dissipative non-adiabatic dynamics. We test the effects on charge separation from varying oscillator strengths, non-adiabatic momentum couplings, the rates of relaxation of excited states coupled to the medium, temperature, and light wavelength. Varying the oscillator strength displays the interplay between competing relaxation and charge transfer dynamics. Varying the non-adiabatic momentum coupling between excited and final states demonstrates the importance of including enough vibrational levels to model the full dynamics of the system and further shows the interplay of relaxation and charge transfer from the final state to the excited state. Larger electron transfer probabilities and longer lasting charge separation occur when oscillator strength into the intermediate state decreases, or when it increases into the final state, and when temperature increases. Longer lasting charge separation also occurs when the non-adiabatic momentum coupling decreases, a somewhat unexpected result which is due to the combined effect of population relaxation and transitions among many vibronic states.