Performance of the semiempirical AM1, PM3, MNDO, and tight-binding methods in comparison with DFT method for the large fullerenes C116-C120

Are the semiempirical methods still reliable for large fullerenes? To answer this question, in this paper, the semiempirical AM1, PM3, MNDO, and tight-binding calculations were performed on the candidate isomers selected from the complete sets of isolated-pentagonrule isomers of C-116-C-120 based on the second generation reactive empirical bond order potential. To assess the reliability of these semiempirical methods and predict the ground-state structures more accurately, the density functional theory calculations at the B3LYP/63-1G(d)//B3LYP/3-21 G level of theory were also carried out on the top 20 low-energy candidates from each semiempirical method. It was found that the tight-binding potential gives a good agreement for the prediction of the relative energies when compared with the B3LYP/ 6-31G* results, while AM1, PM3, and MNDO methods behave badly. Furthermore, we also investigated the structures of the B3LYP/6-31G* low-energy isomers for C-116-C-120 to understand the relationship between the stability and some structural factors. (C) 2007 Elsevier B.V. All rights reserved.