Numerical aspects of real-space approaches to strong-field electron dynamics

Numerical methods for calculating strong-field, nonperturbative electron dynamics are investigated. Two different quantum–mechanical approaches are discussed: the time-dependent Schrödinger equation and time-dependent density functional theory. We show that when solving the time-dependent Schrödinger equation, small errors in the initial ground-state wave function can be magnified considerably during propagation. A scheme is presented to efficiently obtain the ground state with high accuracy. We further demonstrate that the commonly-used absorbing boundary conditions can severely influence the results. The requirements on the boundary conditions are somewhat less stringent in effective single-particle approaches such as time-dependent density functional theory. We point out how results from accurate wave-function based calculations can be used to improve the density functional description of long-ranged, nonlinear electron dynamics. We present details of a method to reconstruct, numerically, the full, unapproximated, Kohn–Sham potential from the density and current of the exact system.