Electron correlation of one-dimensional H2 in intense laser fields:: Time-dependent extended Hartree-Fock and time-dependent density-functional-theory approaches

Ionization and high-order harmonic generation of the one-dimensional (1D) H-2 molecule in intense ultrashort laser fields are investigated using several current approximations for electron dynamics. Single- and double-ionization probabilities are compared with exact results. It is found that for the ground state X (1)Sigma(+)(g), time-dependent extended Hartree-Fock gives generally comparable results except in the plateau region. The adiabatic local density approximation and time-dependent optimized effective potential with self-interaction correction (TDKLI) methods underestimate the ionization probabilities with no plateau and knee for double ionization contrary to the exact results. For the triplet excited state A (3)Sigma(+)(u), where exchange is important, the TDKLI results agree well with the exact results. The exact double-ionization probabilities suggest the need for accurate pair-correlation functions.