Mixed Potential Energy Surfaces of the Ultrafast Isomerization of Retinal in Bacteriorhodopsin Philip J. M. Johnson, Alexei Halpin, Takefumi Morizumi, Valentyn I. Prokhorenko, Oliver P. Ernst and R. J. Dwayne Miller EPJ Web of Conferences, 41 (2013) 07020 Published online: 13 March 2013 DOI: 10.1051/epjconf/20134107020