Temperature-Dependence Of The Positronium Work Function In Aluminum

The electron and positron chemical potentials and their volume derivatives are calculated in Al using the first-principles pseudopotential technique and the frozen-core approximation method, respectively. The positron deformation potential of -8.03 eV obtained by this method agrees very well with that found in other first-principles calculations. The variation of the positronium work function with temperature is calculated by including the thermal lattice vibrations into the electron and position potentials. It is observed that the temperature dependence of the positronium work function does not arise entirely from the volume expansion of the lattice as has been suggested in the past. Proper inclusion of the nonzero-temperature derivative of the positronium work function at constant volume leads to good agreement between the positron deformation potential as obtained from positronium work-function data and present theoretical values.