  A reliable prediction of interatomic force constants in disordered alloys is
an outstanding problem. This is due to the need for a proper treatment of
multisite (atleast pair) correlation within a random environment. The situation
becomes even more challenging for systems with large difference in atomic size
and mass. We propose a systematic density functional theory (DFT) based study
to predict the ab-initio force constants in random alloys. The method is based
on a marriage between special quasirandom structures (SQS) and the augmented
space recursion (ASR) to calculate phonon spectra, density of states (DOS) etc.
bcc TaW and fcc NiPt alloys are considered as the two distinct test cases.
Ta-Ta (W-W) bond distance in the alloy is predicted to be smaller (larger) than
those in pure Ta (W), which, in turn, yields stiffer (softer) force constants
for Ta (W). Pt-Pt force constants in the alloy, however, are predicted to be
softer compared to Ni-Ni, due to a large bond distance of the former. Our
calculated force constants, phonon spectra and DOS are compared with
experiments and other theoretical results, wherever available. Correct trend of
present results for the two alloys pave a path for further future studies in
more complex alloy systems.
