Positron-electron correlation potential

The positron-electron correlation potential outside the metal or semiconductor surface described by the image potential can be written as... 

Comparisons of calculated and measured quenching rates provide a useful measure of the accuracy of the wave function used for the system. As an example, the value of Ze for helium calculated from the zero energy static-exchange wave function of Barker and Bransden (1968) is 0.0347, or 0.0445 when the van der Waals potential is added to the static-exchange equation however, the experimental value obtained by Coleman et al. (1975b) at room temperature is 0.125 0.002 (see section 7.3). This rather large discrepancy, a factor of three, shows that the static-exchange wave function provides a poor representation of the electron-positron correlations in this system. 

The QMC method is ideally suited for mixed systems because electron-positron correlation, which is difficult to treat with Cl methods, is automatically treated correctly. Systems of up to a bit more than ten leptons are routinely treated. Effective core potential methods can be used to extend the method to larger systems. Expectation values of local operators for the distribution k 2 are calculated by straightforward sampling procedures, but nonlocal operators, such as those for the annihilation rate, are problematic and are under active investigation [12],... 

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