  We present an approach to calculate total energies of nanoclusters based on
first principles estimates. For very large clusters the total energy can be
separated into surface, edge and corner energies, in addition to bulk
contributions. Using this separation and estimating these with direct, first
principles calculations, together with the relevant chemical potentials, we
have calculated the total energies of Cu and CdSe tetrahedrons containing a
large number of atoms. In our work we consider polyhedral clusters so that in
addition our work provides direct information on relaxation. For Cu the effects
are very small and the clusters vary uniformly from very small to very large
sizes. For CdSe there are important variations in surface and edge structures
for specific sizes; nevertheless, the approach can be used to extrapolate to
large non-stoichiometric clusters with polar surfaces.
