  The harmonic Kanzaki-Krivoglaz-Khachaturyan model of strain-induced
interaction is generalized to concentrated size-mismatched alloys and adapted
to first-principles calculations. The configuration dependence of both Kanzaki
forces and force constants is represented by real-space cluster expansions that
can be constructed based on the calculated forces. The model is implemented for
the fcc lattice and applied to Cu$_{1-x}$Au$_x$ and Fe$_{1-x}$Pt$_x$ alloys for
concentrations $x=0.25$, 0.5, and 0.75. The asymmetry between the $3d$ and $5d$
elements leads to large quadratic terms in the occupation-number expansion of
the Kanzaki forces and thereby to strongly non-pairwise long-range interaction.
The main advantage of the full configuration-dependent lattice deformation
model is its ability to capture this singular many-body interaction. The roles
of ordering striction and anharmonicity in Cu-Au and Fe-Pt alloys are assessed.
Although the harmonic force constants defined with respect to the unrelaxed
lattice are unsuitable for the calculation of the vibrational entropies, the
phonon spectra for ordered and disordered alloys are found to be in good
agreement with experimental data. The model is further adapted to concentration
wave analysis and Monte Carlo simulations by means of an auxiliary
multi-parametric real-space cluster expansion, which is used to find the
ordering temperatures. Good agreement with experiment is found for all systems
except CuAu$_3$ (due to the known failure of the generalized gradient
approximation) and FePt$_3$, where the discrepancy is likely due to the neglect
of magnetic disorder.
