Excited-state forces within time-dependent density-functional theory: A frequency-domain approach

We introduce a frequency-domain formalism for computing excited-state forces using linear response theory within the framework of time-dependent density-functional theory. We present an implementation of the formalism within a real-space computational framework. We demonstrate the validity and usefulness of the approach by comparing its results to those obtained with a Green's function approach using the GW+Bethe-Salpeter-equation method, for the simple case of the CO molecule. We expect the method to be advantageous for computing excited-state dynamics in large systems.