  Structural and charge relaxation of nanoclusters of CdSe of diameter 1-2 nm
are studied with first principle calculations. The relaxations cause
significant distortions of smaller systems of ~ 1 nm in diameter and have very
minimal effect on the larger systems of ~ 2 nm in diameter. The Cd atoms are
pulled in while the Se atoms are pulled out, which results in the flattening of
Cd-terminated surface and retention of a zig-zag surface for Se-terminated
surface. The surfaces terminated with both Cd and Se result in significant
geometrical distortion resulting in charge concentrations at the distorted
sites. The associated dipole and quadrupole moments are a function of the
distortion or unequal distribution of Cd and Se. The HOMO and HOMO-1 orbitals
are located on or near the distortions. Based on the tetrahedral coordination
and robustness of the core structure to surface relaxation, the approx. 2 nm
diameter NC is the best candidate for building macroscopic structures from NCs.
