Ab Initio Generated UPS of Electron Donors

We have calculated the ultraviolet photoelectron spectra (UPS) data for a variety of molecules that have been suggested for donors for organic photovoltaic materials. The method employed here uses NRLMOL and the PBE-GGA density-functional based method for approximating energies of molecules within a constrained occupation approach. The UPS data is then simulated by calculating the energy difference between the N-electron ground state and a large set of self-consistently generated (N-1)-electron states. Incorporating the relevant absorption probabilities is also discussed. Comparison of calculated UPS spectra to experiment allows us to determine the conditions under which self-interaction corrections$^{1}$ to the energy functional are necessary for determining accurate excitation energies will also be discussed. 1. M. R. Pederson, R. A. Heaton, and C.C. Lin J. Chem. Phys. 82, 2688 (1985).