  Positron lifetimes have been calculated in bulk and monovacancies for most of
the elements of the periodic table. Self-consistent and non-self-consistent
schemes have been used for the calculation of the electronic structure in the
solid, as well as different parameterizations for the positron enhancement
factor and correlation energy. The ratio between the monovacancy and bulk
lifetimes has been analyzed. This ratio shows a periodic behaviour with atomic
number in all the calculation methods and it is in agreement with selected
experimental data. The ratio shows, in contradiction to previous assumptions,
sensitiveness to the approximations used in the calculations. This extensive
work has allowed us to study and enlighten features of the theory and computing
methods broadly used nowadays in simulating, studying and understanding
positronic parameters.
