Geometry Optimisation with CASTEP
Geometry Optimisation with CASTEP
Geometry Optimisation with CASTEP
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thickness<br />
We can see that the total energy is converged <strong>with</strong> respect to the vacuum gap when this has a thickness<br />
greater than about 7 Å (there is a slight upwards kink after this). We will use a 9 Å vacuum gap in all<br />
future calculations.<br />
Now it remains to converge the basis set paramters. Cutoff energies of 140, 180, 230, 260, 290, 320, 350,<br />
and 370eV were used <strong>with</strong> MP grids containing 4, 8 and 9 k-points. The calculations were performed on<br />
a Beowulf cluster using 8 nodes for the 4 and 8 k-point calculations and 9 nodes for the 9 k-point<br />
calculation. The convergence of the total energy <strong>with</strong> basis set parameters is shown below.<br />
Figure 10:Convergence of the total energy <strong>with</strong> respect to the basis<br />
set parameters<br />
We can see that using 9 layers of silicon, a 9 Å vacuum gap, 9 k-points and a 370 eV cutoff energy will<br />
ensure minimisation of systematic errors <strong>with</strong> respect to both supercell aperiodicity and the basis set<br />
repectively.<br />
So what results do we get? Click on the movie below to see the evolution of the atomic positions as the<br />
calculation progresses. Please use the 'back' button to close the movie.
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