In all the latter calculations, the SCF convergence threshold was settled at 10 -9 Hartree, while the geometry optimization was considered achieved when maximum atomic forces and atomic displacement were both below 10 -4 Bohr and 10 -4 Hartree/Bohr, respectively. QUICKSTEP makes use of a multi-grid system to regulate the accuracy of the calculations: 4 grids with a cut-off of 900 Ry on the main grid and a relative cut-off of 100 Ry were enough to optimize most of the structures and to performs AIMD on them. To fully optimize all the structures, a more accurate multigrid was required, formed by 5 grids, a main cutoff of 1800 Ry and a relative cutoff of 300 Ry.