An FDTD-TDDFT method for the EM/QM co-simulation of nanowire systems in the Lorenz gauge

Abstract

Real-time time-dependent density functional theory (TDDFT) constitutes a cornerstone in the modeling of nanoscale materials. Although numerous application areas have already benefited from the technique, investigation of both forward and backward coupling in matter systems subject to a vectorial electromagnetic (EM) perturbation remains challenging. To address this problem, this work proposes a modeling framework leveraging the finite-difference time-domain algorithm for determining the scalar and vector potential from the EM fields, both in the traditional Coulomb gauge as well as the nearly unexplored Lorenz gauge. Using the latter allows for a straightforward calculation of the electromagnetic vector potential, a natural implementation of perfectly matched layers, and a significant reduction in computation time. To describe the pertaining quantum-mechanical (QM) dynamics, a real-space and full-potential formulation of TDDFT has been utilized. Furthermore, a multistep algorithm is leveraged to bridge the gap between the stability limits of the EM and QM subsystems. The method is applied to practical nanowire topologies to demonstrate its versatility. The results exhibit an excellent correspondence between both gauges, while highlighting the superior numerical performance of the Lorenz gauge technique.