Be(Al,Cr,FeIII)2O4 solid solutions has been analyzed using a previously elaborated set of interatomic potentials for
atomistic modeling of simple and complex beryllium oxides, which almost exactly reproduced their structural, elas-
tic, and thermodynamic properties. Calculations have been performed for a (4a
2b 2c) supercell of the olivine structural type with the relieved nontranslational symmetry (space group P1), which has made it possible to specify
the distribution of trivalent atoms over nonequivalent positions and to provide relaxation of the local structure. The
mixing properties have been calculated over the entire range of compositions, the changes in the Gibbs free energy
with variations in temperature and the regions of stability of the solid solutions have been estimated, and the critical
values of the temperature and composition have been determined. The histograms of the distributions of M–M, M–
O, and O–O interatomic distances, as well as MO6 octahedron volumes, have been constructed; the compliances of
cation positions have been evaluated; and the groups of atoms that are most readily shiftable from their ideal positions
have been established. The performed analysis has demonstrated that two different octahedral positions M1 and M2
in the olivine-type structure, namely, chrysoberyl, are extremely sensitive to their own atomic environment. This leads
to a preferable incorporation of Al3+ cations into the M1 octahedral position, whereas larger-sized Cr3+ (Fe3+) cations
preferentially occupy the M2 octahedral position.