Towards efficient ab initio calculations of electron scattering by polyatomic molecules: II. Efficient evaluation of exchange integrals

In this paper it is shown that the complex Shavitt functions F(n)(z) can be interpolated in the same way as the real Shavitt functions F(n)(x) in electronic structure theory. This greatly accelerates the evaluation of exchange integrals in a mixed Gaussian and plane-wave basis. Together with other approximations reported previously this extends applications of ab initio calculations of electron scattering to larger molecules. The performance of the new program was tested for elastic scattering on a training set of eight molecules: H(2)O, CH(4), CF(4), ethylene, propane, cyclopropane, benzene and uracil. The vibrational electron energy loss spectra of benzene and uracil were calculated as an example to show that ab initio calculations are now feasible on a desktop computer for molecules of that size.