1. A computer system comprising: a processor configured to execute: a finite element model (FEM) module to determine a FEM that models an implanted electrode and a tissue medium in which the electrode is implanted; a Fourier FEM solver module to calculate a potential distribution in the tissue medium using information from the FEM module and a capacitive component of at least one of the electrode and the tissue medium; and a volume of activation (VOA) module to provide a predicted VOA using the potential distribution and a neuron model.