**3.1 Optimization of the diamond structure**

The diamond unit cell contains two carbon atoms located at (0.0, 0.0, 0.0) and (0.25 a, 0.25 a, 0.25 a). After optimization, the CC bond length was found to be 1.55 Å. Relaxation of all model systems was performed using an 8 8 8 Monkhorst-Pack grid sampling, used during Brillouin zone integrations (512 k-points in the irreducible part of the Brillouin zone). **Tables 2** and **3** shows the results of the diamond structure optimization.

Other results provided by GPAW: C-setup: Name: Carbon. Z: 6. Valence: 4. Core: 2. Charge: 0.0. Cutoffs: 0.64(comp), 1.14(filt), 1.14(core), lmax = 2.
