  Light alkali metals have usually been considered as simple metals due to
their monovalency and high conductivity. In these metals ionic pseudopotentials
are weak and the nearly free electron model (NFE) becomes quite accurate at
normal conditions. However, very recent experiments have shown that at high
pressures their electronic properties deviate radically from the NFE model and
even become unexpected good superconductors. In this work we present ab initio
calculations to analyze the deviation from simplicity in a lithium monolayer
(ML) when pressure is applied. We have seen that as a result of the increasing
non-local character of the atomic pseudopotential with increasing pressure, the
surprising half filling Hubbard-type nesting observed in the Fermi line can
explain the interesting complex behavior in lithium ML, induced by its
correlated structural, electronic and even magnetic properties.
