Photoionization calculations in molecules using an overset grid implementation*

The ultrafast electronic processes in molecules demand, theoretically, the challenging representation of the correlated short-range structure and the asymptotic highly oscillatory behavior of an electron in the continuum at the same time. We solve these requirements using an overset grid implementation, that consist of a central grid and multipole atom-center subgrids, allowing a simultaneous spherical expansions of the wave function about the multiple centers, which together with the Complex Kohn variational method, has proven to be effective in electron-neutral scattering problems, in which applying repeatedly the free particle Green function and potential $\hat{G}_0^+\hat{V}$ onto the channel Bessel function, leads to a Pad\'{e} approximant to the T-matrix. We have extended this formalism to photoionization problems by imposing a fixed spherical boundary matches to Coulomb boundary conditions in the outer region as well as adding a pseudo-potential to enforce orthogonality to the occupied orbitals of the target. We show the performance of the method by computing the valence photoionization cross sections of N$_2$, CF$_4$, SF$_6$ and their electron angular distributions.