The role of orthorhombic distortions in gallium under high hydrostatic pressure

We have performed a detailed analysis of the double-well feature of the total energy for the Ga-III phase as a function of tetragonal and orthorhombic distortions of the face-centered cubic (fcc) lattice. We demonstrate that in the low-pressure region this double-well feature disappears and only one minimum exists. In order to reveal this result, the possibility of orthorhombic distortions has to be taken into account. At elevated pressure between 58 and 84 GPa, the second minimum becomes pronounced, but never develops into a separate local minimum up to the transformation into the fcc phase.