  We study how the Mott metal-insulator transition (MIT) is influenced when we
deal with electrons with different angular momenta. For lithium we found an
essential effect when we include $p$-orbitals in the description of the Hilbert
space. We apply quantum-chemical methods to sodium rings and chains in order to
investigate the analogue of a MIT, and how it is influenced by periodic and
open boundaries. By changing the interatomic distance we analyse the character
of the many-body wavefunction and the charge gap. In the second part we mimic a
behaviour found in the ionic Hubbard model, where a transition from a band to a
Mott insulator occurs. For that purpose we perform calculations for mixed
sodium-lithium rings. In addition, we examine the question of bond alternation
for the pure sodium system and the mixed sodium-lithium system, in order to
determine under which conditions a Peierls distortion occurs.
