Positron-electron correlations near a metal surface and the local density approximation

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Abstract
The electron distribution around a positron near a metal surface has been calculated in the random-phase approximation. The positron was treated as a free particle, and the infinite barrier model was used for the electrons. As a positron approaches a metal surface and passes out of the electron gas, the spherical polarisation cloud distorts and becomes the image charge spread out across the surface, in a similar manner to the exchange-correlation hole of an electron. The positron-electron correlation energy and the positron annihilation rate have been calculated as functions of the positron position and compared with the results of the local density approximation. The agreement is good in the region of finite electron density.