A calculation of the coefficient Ck of the terms linear in k in the Gamma 8 valence bands of several III-V semiconductors is presented. On the basis of the systematics of these results it is concluded that these terms arise from coupling by the linear momentum and the spin-orbit operators to the upper-most d levels of the core. A simple analytic expression to calculate Ck for all III-V, II-VI, and I-VII compounds with zinc-blende structure is proposed. The results are in good agreement with the few experimental data available.
 

Physical Review Letters, 56 2831-3, 1986.