  Silicon carbide is a hard, semiconducting material presenting many polytypes,
whose behavior under extreme conditions of pressure and temperature has
attracted large interest. Here we study the mechanical properties of 3C-SiC
over a wide range of pressures (compressive and tensile) by means of molecular
dynamics simulations, using an effective tight-binding Hamiltonian to describe
the interatomic interactions. The accuracy of this procedure has been checked
by comparing results at T = 0 with those derived from ab-initio
density-functional-theory calculations. This has allowed us to determine the
metastability limits of this material and in particular the spinodal point
(where the bulk modulus vanishes) as a function of temperature. At T = 300 K,
the spinodal instability appears for a lattice parameter about 20% larger than
that corresponding to ambient pressure. At this temperature, we find a spinodal
pressure P_s = -43 GPa, which becomes less negative as temperature is raised
(P_s = -37.9 GPa at 1500 K). These results pave the way for a deeper
understanding of the behavior of crystalline semiconductors in a poorly known
region of their phase diagrams.
