SINGLE AND DOUBLE PHOTOIONIZATION FROM DIPOLE RESPONSE FUNCTION

A method for including the correlated motion of the electrons in the c alculation of single and double ionization of atomic and molecular sys tems by the absorption of a single photon is described. The correlated dipole response function is central to the formulation. The single an d double photoionization cross sections of helium are calculated. We s how that the method accurately corrects for the error that is present at high energies when the length gauge is used to characterize the pho ton interaction. The cross sections obtained from the length, velocity , and acceleration gauges are brought into agreement with each other a nd with cross sections calculated from the many-body perturbation theo ry.