Work Functions for Positrons in Metals

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Abstract
Positron work functions have been calculated for a number of simple metals and the noble metals. Three separate contributions were estimated: the positron zero-point energy and the positron-electron correlation energy, which together constitute the internal positron chemical potential, and the contribution from the surface-dipole layer. The effect of the ionic lattice was included in the zero-point energy and the surface-dipole barrier. The correlation energy was calculated taking into account the nonlinear response of the electron system to the positron. Of all the metals considered only Au and Cu were calculated to have negative work functions. Positronium work functions were also calculated and in all cases they are smaller than the corresponding positron work function and negative for several metals.