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A colleague and I were recently discussing some calculations on relaxation and molecular dynamics of slabs under the use of an electric field (using the saw-tooth implementation of EFIELD / LDIPOL). From my reading through of the manual and also the code (specifically in dipol.F), the only contribution to the forces is through the dipole term added to the electronic contribution in the Hellman-Feynman forces. However, as far as I'm aware, there is no inclusion of the force due to the direct interaction of the electric field with the pseudo-nuclei. Is there a reasonable straightforward way to include this interaction even at a semi-classical level? Otherwise, is it correct to assume that nuclei only move due to their following the perturbation of the electron charge density due to the field? Thanks for any advice!