  Using the renormalized quasiparticle random phase approximation (RQRPA), we
calculate the light neutrino mass mediated mode of neutrinoless double beta
decay of Ge76, Mo100, Te128 and Te130. Our results indicate that the simple
quasiboson approximation is not good enough to study the neutrinoless double
beta decay, because its solutions collapse for physical values of g_pp. We find
that extension of the Hilbert space and inclusion of the Pauli Principle in the
QRPA with proton-neutron pairing, allows us to extend our calculations beyond
the point of collapse, for physical values of the nuclear force strength. As a
consequence one might be able to extract more accurate values on the effective
neutrino mass by using the best available experimental limits on the half-life
of neutrinoless double beta decay.
