Real time calculation of optical spectra of atomic clusters using time dependent local density approximation (LDA)

Theory The optical properties of a molecule are obtained from its response to a perturbing electric field. In our case, the electric field is chosen to be a step function E(t) = E0 1−θ(t) ( ) (1.) where θ(t) is the unit step function. The perturbing field displaces the electrons of the molecule, which gives rise to a time varying electric dipole by means of which optical properties can be obtained. For t<0, the molecule is put in a constant electric field and the system is solved for the ground state. At t=0, the perturbing field is switched off and Schrödinger’s equation ih ∂ ∂t Ψ = HΨ (2.)