Johannes is a Professor in Theory and Simulation of Materials in the Department of Materials at Imperial College London. He is also the Director of the MSc in Advanced Material Science and Engineering and Imperial's director of the Thomas Young Centre for Theory and Simulation of Materials and Molecules. He obtained a Ph.D. in Physics from Cornell University in 2010. Before joining Imperial in 2014 as a Royal Society University Research Fellow, he was a postdoctoral researcher at UC Berkeley and Lawrence Berkeley National Lab.

His research is focused on electronic excitations in complex materials. Recently, his group has developed novel methods to model excited states in twisted bilayers of two-dimensional materials, such as twisted bilayer graphene and twisted homo- and heterobilayers of transition metal dichalcogenides. Other areas of interest include hot carrier generation in nanoplasmonic materials and simulating core and valence electron spectroscopies via the GW and GW cumulant approach or the Delta-SCF method.