Density‐Functional Approach to Atoms in Strong Laser Pulses

Abstract A density functional formalism for time‐dependent systems comparable to the theory of Hohenberg, Kohn and Sham is presented. In this approach, the time‐dependent density can be obtained (in principle exactly) from a set of time‐dependent single‐particle (Kohn‐Sham) equations. In order to apply the time‐dependent Kohn‐Sham scheme in practical calculations, an effective time‐dependent single‐particle potential is needed. Given an expression for the quantum mechanical action A [ø 1 …ø N ] of an N ‐electron system as a functional of N time‐dependent orbitals, we present a method of constructing the variationally best local time‐dependent single‐particle potential which, when inserted in a time‐dependent single‐particle Schrödinger equation yields orbitals {ø j } that make A [ø 1 …ø N ] stationary. We also propose a simplification of this scheme leading to a time‐dependent generalization of the static optimized effective potential recently introduced by Krieger, Li and Iafrate [Phys. Lett. A 146 , 256 (1990)]. Applications of this scheme to the case of a beryllium atom in a strong laser pulse are presented.