The generalised pseudoatom potential in solids: relation to screening and lattice dynamics

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Abstract
The change in potential when an ion is displaced is shown to have pseudoatom qualities i.e. total potential can be divided exactly into atomic-like potentials which move rigidly with the ions to first order in the displacement. An additional non-rigid potential arises under the ionic distortion. Relations between the pseudoatom potential and the pseudoatom charge density of Ball (1975), which is mathematically similar, are pointed out. Some previous approximations to the dielectric screening are shown to be inconsistent; it is suggested that, for transition metal systems, a consistent treatment of the pseudoatom potential may be necessary to achieve further progress. This pseudoatom behaviour of the potential will have consequences for lattice dynamics and the electron-phonon interaction.