Structural, mechanical, and vibrational properties of Ga1-xInxAs (0≤x≤1) random solid solutions are investigated with classical and ab initio molecular-dynamics simulations. We find that the Ga–As and In–As bond lengths change only slightly as a function of x, despite the large lattice mismatch (∼7%) between GaAs and InAs crystals. The nearest cation–cation distance has a broad distribution, whereas the nearest neighbor anion–anion distance distribution has two distinct peaks. The elastic constants exhibit a significant nonlinear dependence on x. The phonon density-of-states exhibits two high-frequency optical modes. These results are in excellent agreement with experiments. © 2003 American Institute of Physics.