  We present calculations of the exchange interactions and Curie temperatures
in Cr-based pnictides and chalcogenides of the form CrX with X=As, Sb, S, Se
and Te, and the mixed alloys CrAs$_{50}$X$_{50}$ with X=Sb, S, Se, and Te. The
calculations are performed for Zinc Blende (ZB) structure for 12 values of the
lattice parameter between 5.44 and 6.62 \AA, appropriate for some typical II-VI
and III-V semiconducting substrates. Electronic structure is calculated via the
linear muffin-tin-orbitals (LMTO) method in the atomic sphere approximation
(ASA), using empty spheres to optimize ASA-related errors. Whenever necessary,
the results have been verified using the full-potential version of the method,
FP-LMTO. The disorder effect in the As-sublattice for CrAs$_{50}$X$_{50}$
(X=Sb, S, Se, Te) alloys is taken into account via the coherent potential
approximation (CPA). Exchange interactions are calculated using the linear
response method for the ferromagnetic (FM) reference states of the alloys, as
well as the disordered local moments (DLM) states. These results are then used
to estimate the Curie temperature from the low and high temperature side of the
ferromagnetic/paramagnetic transition. Estimates of the Curie temperature are
provided, based on the mean field and the more accurate random phase
approximations. Dominant antiferromagnetic exchange interactions for some low
values of the lattice parameter for the FM reference states in CrS, CrSe and
CrTe prompted us to look for antiferromagnetic (AFM) configurations for these
systems with energies lower than the corresponding FM and DLM values. Results
for a limited number of such AFM calculations are discussed, identifying the
AFM[111] state as a likely candidate for the ground state for these cases.
