Table 3.

Comparison of the effect of different force field based preconditioners for the geometry optimisation of organic molecules in gas phase (total number function/gradient calls). Convergence threshold was $\parallel \nabla E{\parallel }_{\infty }={10}^{-4}$ eV Å⁻¹ for all cases.

System (# of atoms)	ID	FF/GAFF	FF/UFF	FF/LFF
5-nitrobenzisoxazole (16)	89	25	31	34
menthone (29)	207	29	39	39
alanine tripeptide (32)	395	77	79	90
thc (53)	720	84	77	92
heme (75)	500	175	219	n.a.
taxol (113)	1662	419	393	400
16-mer polyalanine (172)	3549	348	280	273