Dressed states of the high-frequency Floquet theory for atoms and molecules with standard computational quantum chemistry programs

The multipole expansion of the electron - nucleus interaction in the so-called high-frequency limit of the Floquet theory in the Kramers - Henneberger frame is used to determine equivalent point-charge distributions. This allows the use of standard quantum chemistry programs to calculate the energies. It is found that satisfactory results can be obtained with a quadrupole approximation if the parameter ( , amplitude of electric field; , frequency of the field) does not exceed 30 au. The examples which are treated are the hydrogen atom, the hydrogen negative ion and the hydrogen molecular ion , systems for which accurate results are available.