GENERALIZED FLOQUET THEORETICAL FORMULATION OF TIME-DEPENDENT DENSITY-FUNCTIONAL THEORY FOR MANY-ELECTRON SYSTEMS IN MULTICOLOR LASER FIELDS

We generalize the Floquet formulation of the time-dependent density fu nctional theory (TDDFT) [Telnov and Chu, Chem. Phys. Lett. 264, 466 (1 997)] to the case of many-electron systems in multicolor or polychroma tic time-dependent fields. It is shown that the time-dependent Kohn-Sh am equations can be transformed into an equivalent time-independent in finite-dimensional Floquet Hamiltonian eigenvalue problem. For the cas e of bound-free transitions, we introduce the notion of complex densit y and present a non-Hermitian many-mode Floquet formulation of TDDFT. A procedure is presented for the determination of the complex quasi-en ergies and the calculation of the total and partial ionization rates f rom individual electron orbitals. The theory is illustrated by a case study of multiphoton ionization of He atoms in the presence of an inte nse 248 nm laser field and its third harmonic. Novel intensity- and ph ase-dependent behavior of multiphoton processes in two-color fields is reported. (C) 1998 John Wiley & Sons, Inc.