Abstract
Calculations based on a tight binding model of energy bands in the alloy system CdxHg1-xTe are reported and the results used to discuss observed changes in the optical transitions in these alloys. Large effects due to changes in the relativistic terms in the Hamiltonian are found to be the main cause of energy changes and the disappearance of the direct energy gap at a concentration of 84% Hg. More detailed changes in the observed transition energies are discussed in terms of disorder effects in the alloys.