An assessment of semiempirical (MNDO, AM1 and PM3) methods to model buckybowls

Semiempirical MNDO, AM1 and PM3 calculations are performed to estimate the bowl-to-bowl inversion barrier, equilibrium geometries, curvature, and some other physico-chemical properties, for about fifteen buckybowl molecules, including diversified classes such as corannulene, sumanene, canastanes and semibuckminsterfullerenes. The ability of these three economical methodologies in getting quantitative estimates for the bowl-to-bowl inversion barrier is assessed. The suitability of each of these semiempirical methods for obtaining equilibrium geometries, by doing single point energy calculations at higher levels, the curvature and the ionization potential is assessed by comparison of these values with the available experimental and higher level computational methods. This study unequivocally indicates that MNDO is better than AM I and PM3, for the bowl-to-bowl inversion barrier. Although, the equilibrium geometries obtained at PM3 level seem to be better suited for single point calculations at higher levels of theory, the structural parameters do not show clear preference to any of the methods. The present study concludes that MNDO is a better choice in modeling the inversion dynamics of buckybowls among the popular semiempirical methodologies. (C) 2002 Elsevier Science B.V. All rights reserved.