Solution energies of tetravalent dopants in metallic $VO_{2}$

The stability of three dopants has been examined for $VO_{2}$. The room temperature phase is metallic and hence a dense k-mesh is required for the calculations of pure and doped $VO_{2}$.
Using k-point parallelism in VASP, Dr Grau-Crespo tested $4\times4\times4$ (18 irreducible k-points) and $8\times8\times8$ (75 irreducible k-points) meshes for pure $VO_{2}$. The latter calculation was performed over 360 processors in the HECToR Phase2b supercomputer, with a speedup factor of 13 compared to the standard version running on 24 processors (ideal scaling would correspond to a speedup factor of 15). The calculations of the doped cell were performed on 168 processors, with KPAR=7 groups (of 3 k-points each) running in parallel, on 24 processors each. All geometries were optimised until the forces on the ions were all less than 0.01 eV/Å.