Carbon 8 layer system with one atom displaced

 

This system was obtained from David Roundy who was using it for a frozen phonon calculation. The system has 16 layers (atoms) extended in the (214) direction. One atom at one end is displaced by ~1.5 Bohr in the (214) direction. We use a k-point sampling of a 4x4x1 Monkhorst-Pack mesh. As long as a value of submatrix_energy_cutoff = 10 is used, then the direct minimization method gives the best performance. Of the SCF methods, the Pulay-Kerker is best. This is because the system is not large enough or inhomogeneous enough for the Pulay-Thomas-Fermi charge mixing to be necessary.

 

 

 

 

Fig. 1 convergence of different methods to obtain the total energy