  A possible solution for the problem of memory-size and computer-time, is the
extrapolation of basis-set$^1$. This extrapolation has two exponents $\alpha$
and $\beta$, corresponding to the HF (reference energy) and the energy of
correlations (EC), respectively. For a given system, the exponents are taken as
constant$^2$, and potential energy surfaces (PES) are generated. We have found
that the values of $\alpha$ and $\beta$ are not constant, but vary from
position to position in the system. How to deal with such situation and get
very accurate PES, is discussed.
