  We present {\it ab initio} total energy and band structure calculations based
on Density Funtional Theory (DFT) within the Local Density Aproximation (LDA)
on group-V mixing effects in the optoelectronic material
$(ZnSi)_{1/2}P_{1/4}As_{3/4}$. This compound has been recently proposed by
theoretical design as an optically active material in the 1.5 $\mu$m (0.8 eV)
fiber optics frequency window and with a monolithic integration with the Si
(001) surface. Our results indicate that alloy formation in the group V planes
would likely occur at typical growth conditions. In addition, desired features
such as in-plane lattice constant and energy gap are virtually unchanged and
the optical oscillator strength for band-to-band transitions is increased by a
factor of 6 due to alloying.
