| Abstract: | The LCMTO (linear combination of muffin-tin orbitals) technique has been used to calculate the first temperature dependent energy bands for a transtion metal compound. The particular compound studied was hexagonal NiS which undergoes a first-order metal-to-nonmetal transition as the temperature is lowered below 264K. We find the bands to agree well with XPS data and that the Sp bands overlap the bottom of the d bands as predicted by White and Mott. This p-d overlap, which reduces the correlation energy, is found to increase with temperature as a result of lattice vibrations whereas the lattice distortion accompanying the transition has very little effect on the energy bands. This suggests that the Mott-Hubbard transition in NiS is driven by the Debye-Waller modification of the potential and not the lattice distortion as suggested by White and Mott. |
