Time-dependent unrestricted Hartree-Fock theory for the multiphoton ionization of atoms

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Abstract
Time-dependent unrestricted Hartree-Fock (TDUHF) theory is formulated for the multiphoton ionization of a model atom. The single-particle states are nonorthogonal and the quantum variational principle requires additional normalization terms. For a model He atom, the three-dimensional (3D) electrostatic interaction is replaced by a 1D soft-core interaction that allows the construction of the two-electron atom in only two dimensions. The resulting 1D formulation of the TDUHF equations contains numerous exchange and overlap terms. The TDUHF multiphoton ionization rates are found to be in better agreement with the results of a direct solution of the time-dependent Schrödinger equation on a 2D lattice than the rates predicted by a 1D formulation of the standard TDHF equations.