Particle number projection in the macroscopic–microscopic approach

We perform nuclear ground-state pairing calculations with the monopole pairing interaction. The particle number fluctuations are taken into account by the particle number projection method, with variation after projection. The pairing-correction energies obtained in this approach are compared to the BCS-model results. We discuss extensively how to properly incorporate different pairing models in global macroscopic–microscopic nuclear mass calculations. A method to calculate the smoothly changing part of the particle number projected energy is developed based on the Strutinsky procedure, making it possible to extract a pairing-shell energy. The behavior of the different pairing models is investigated in detail in the nuclei 164Er and 165Tm. Calculations are then performed along the β-stability line and for several isotope and isotone chains from the proton drip-line to the neutron drip-line. The single-particle energy levels used are obtained from two different single-particle potentials: the folded-Yukawa and the modified-harmonic oscillator potentials. The pairing calculations in the two potentials differ slightly in the fine-structure but the overall results are very similar. When comparing the particle number projected model and the BCS model it is found that the pairing-shell energy is quite insensitive to which microscopic pairing model is used.