TDDFT–Generalized kick perturbations and monitoring observables for calculation of excitation energies

Abstract

This article introduces a generalized way to calculate excitation energies of many-body Hamilton operators by propagating kicked orbitals within time-dependent density functional theory (TDDFT). We use generalized δ(t) perturbations and monitor certain observables of the reduced one-body density to calculate the excitation energies of a static many-particle problem. This generalizes the usual procedure of a linear momentum kick and monitoring the induced t-dependent dipole moment or higher moments. In particular we propose to monitor the time-dependent local charges (e.g. Voronoi, …) in a molecule. As a simple application the S = 0 singlet excitation spectrum of helium is calculated with this formalism included in a standard TDDFT-software package for atoms, QPROP.