$\gamma$-$\alpha$ iso-structural Transition in Cerium*

We present zero-temperature first-principle calculations of elemental cerium, and we compute its pressure-volume phase diagram within a theoretical framework able to describe simultaneously both the $\alpha$ and the $\gamma$ phase. A surprising result revealed by our study is the presence of a clear signature of the transition at zero temperature, and that this signature can be observed if and only if the spin-orbit coupling is taken into account. Our calculations indicate that the transition line in the pressure-temperature phase diagram of this material has a low-$T$ critical point at negative pressures, placed very close to zero temperature. This suggests that cerium is very close to being ``quantum critical'', in agreement with recent experiments.