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Comparison of model exchange potentials for low-energy e-H2 collisions with and without polarisation effects

The utility of several model exchange potentials in e-H2 scattering calculations from 0.01-1.00 Ryd is investigated. Model potential cross sections and eigenphase sums for the 2 Sigma g, 2 Pi g, 2 Sigma u and 2 Pi u e-H2 symmetries are calculated both with and without polarisation. Their validity is assessed from a comparison with results obtained when exchange is treated via an exact iterative procedure. To ensure meaningful comparisons, the same static and polarisation potentials are used for the model exchange and exact exchange calculations. Results obtained with the tuned free-electron-gas exchange potential are consistently found to have the best overall agreement with exact exchange values. In addition, new exact static exchange polarisation results are reported.