  Electronic-structure methods based on density-functional theory (DFT) were
used to directly quantify the effect of chemical short-range order (SRO) on
thermodynamic, structural, and electronic properties of archetypal
face-centered-cubic (fcc) Cu$_{3}$Au alloy. We show that SRO can be tuned to
alter bonding and lattice dynamics (i.e., phonons) and detail how these
properties are changed with SRO. Thermodynamically favorable SRO improves phase
stability of Cu$_{3}$Au from -0.0343 eV-atom$^{-1}$ to -0.0682 eV-atom$^{-1}$.
We use DFT-based linear-response theory to predict SRO and its electronic
origin, and accurately estimate the transition temperature, ordering
instability (L1$_2$), and Warren-Cowley SRO parameters, observed in
experiments. The accurate prediction of real-space SRO gives an edge over
computationally and resource intensive approaches such as Monte-Carlo methods
or experiments, which will enable large-scale molecular dynamic simulations by
providing supercells with optimized SRO. We also analyze phonon dispersion and
estimate the vibrational entropy changes in Cu$_{3}$Au (from 9k$_{B}$ at 300 K
to 6$k_{B}$ at 100 K). We establish from SRO analysis that exclusion of
chemical interactions may lead to a skewed view of true properties in
chemically complex alloys. The first-principles methods described here are
applicable to any arbitrary complex solid-solution alloys, including
multi-principal-element alloys, so hold promise for designing technologically
useful materials.
