Particle number projection on a spatial domain

Abstract

The formalism of particle number on a spatial domain for mean field wave functions with pairing is revisited to account for the case where finite dimensional basis are used. The formulas differ from the ones previously used in the literature. It is shown that the present formalism has the right limit in the well known case of zero pairing whereas the other formalism do not satisfy this basic requirement. By using a simple one-dimensional model we illustrate the differences in the results for particle number distribution probability obtained with the two methods.