Table 6.

Total number of function/gradient calls geometry optimisation steps of bulk silicon and a bulk silicon vacancy using different preconditioning strategies. Convergence criterion was $\parallel \nabla E{\parallel }_{\infty }={1.0}^{-3}$ eV Å⁻¹.

System (# of atoms)	Bulk geometry optimisation			Vacancy geometry optimisation
	ID	Exp	FF/UFF	ID	Exp	FF/UFF
2 × 2 × 2 (64)	32	17	10	34	15	9
4 × 4 × 4 (512)	63	18	10	57	16	9
8 × 8 × 8 (4096)	105	21	13	96	17	11
16 × 16 × 16 (32768)	147	35	21	142	19	11