  In a previous work one of the authors proposed a simple model for studying
systems under pressure based on the Thomas-Fermi (TF) model of single atom. In
this work we intend to extend the previous work to more general Thomas-Fermi
models where electronic exchange and correlation are introduced. To do so, we
first study numerically the equation obtained by H.W.Lewis (TFDL) which
introduces the effects of exchange and correlation into the original TF
equation; next the procedure followed in the previous work is extended to the
new approach and a specific example is illustrated. Although one could expect
that no big differences were produced by the generalized TF model, we show the
qualitative as well as quantitative equivalence with detailed numerical
results. These results support the robustness of our conclusions with regards
to the model proposed in the previous work and give the character of
universality (i.e. to pass from one atom to another, the quantities calculated
must be simply scaled by a numerical factor) to the properties of compressed
systems shown in this work.
