The separable representation of exchange in electron scattering from polyatomic targets

We present a new computational implementation of a discrete-basis representation for the bound-continuum exchange interaction in electron scattering from polyatomic targets of arbitrary geometry. Both bound and continuum electrons are described within a single-centre expansion framework, the ensuing static interaction is obtained exactly and correlation-polarization effects are included via a parameter-free, density-functional-based model potential. Coupled scattering equations are solved efficiently using a Volterra integral form and convergence tests on the size of the additional basis needed to represent exchange forces are carried out extensively for H2O and O-3 as benchmark systems.