  The nucleon single-particle energies (SPEs) of the selected nuclei, that is,
16O, 40Ca, and 56Ni, are obtained by using the diagonal matrix elements of
two-body effective interaction, which generated through the lowest order
constrained variational (LOCV) calculations for the symmetric nuclear matter
with the AV18 phenomenological nucleon-nucleon potential. The SPEs at the major
levels of nuclei are calculated by employing a Hartree-Fock inspired scheme in
the spherical harmonic oscillator basis. In the scheme, the correlation
influences are taken into account by imposing the nucleon effective mass factor
on the radial wave functions of the major levels. Replacing the
density-dependent one-body momentum distribution functions of nucleons,
n(k,rho), with the Heaviside functions, the role of n(k,rho) on the nucleon
SPEs at the major levels of the selected closed shell nuclei, is investigated.
The best fit of spin-orbit splitting is taken into account when correcting the
major levels of the nuclei by using the parameterized Wood-Saxon potential and
the AV18 density-dependent mean field potential which is constructed by the
LOCV method. Considering the point-like protons in the spherical Coulomb
potential well, the single-proton energies are corrected. The results show the
importance of including n(k,rho), instead of the Heaviside functions, in the
calculation of nucleon SPEs at the different levels, particularly the valence
levels, of the closed shell nuclei.
