Sattelmeyer Kurt W, Tubert-Brohman Ivan, Jorgensen William L
Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520.
J Chem Theory Comput. 2006 Mar;2(2):413-9. doi: 10.1021/ct050174c.
The effect of reintroducing the overlap matrix into the secular equations for an NDDO (neglect of diatomic differential overlap)-based semiempirical molecular orbital method has been investigated. The modification is expected to improve the description of interactions between electron pairs. The idea has been tested by implementation and evaluation of a nonorthogonal version of the MNDO method (NO-MNDO) with parametrization for hydrogen, carbon, nitrogen, and oxygen. Overall, the accuracy of NO-MNDO for heats of formation is nearly identical to that for the more highly parametrized AM1 method. The mean absolute error (MAE) for heats of formation of a comprehensive set of 622 neutral, closed-shell molecules is reduced from 8.4 kcal/mol with MNDO to 6.8 kcal/mol with NO-MNDO. In addition, the performance for conformational equilibria and torsional barriers is significantly improved with NO-MNDO, presumably owing to the improved description of closed-shell interactions. For molecular geometries, the usual training and test sets have been expanded through use of MP2/6-31G(d) results for consistent comparisons. The performance of NO-MNDO for bond lengths, bond angles, and dihedral angles remains good with MAEs of 0.017 Å, 2.5°, and 4.5°. Additionally, NO-MNDO corrects severe errors by MNDO for R(•) + H-R' hydrogen-atom transfers, while testing for activation barriers for nine pericyclic reactions reveals only modest improvement.
研究了将重叠矩阵重新引入基于忽略双原子微分重叠（NDDO）的半经验分子轨道方法的久期方程中的效果。预计这种修改将改善对电子对之间相互作用的描述。通过实施和评估具有氢、碳、氮和氧参数化的非正交MNDO方法（NO-MNDO）对这一想法进行了测试。总体而言，NO-MNDO在生成热方面的准确性与参数化程度更高的AM1方法几乎相同。对于一组622个中性闭壳分子的生成热，平均绝对误差（MAE）从MNDO的8.4 kcal/mol降低到NO-MNDO的6.8 kcal/mol。此外，NO-MNDO在构象平衡和扭转势垒方面的性能显著提高，可能是由于对闭壳相互作用的描述得到了改善。对于分子几何结构，通过使用MP2/6-31G(d)结果进行一致比较，扩展了常用的训练集和测试集。NO-MNDO在键长、键角和二面角方面的性能仍然良好，MAE分别为0.017 Å、2.5°和4.5°。此外，NO-MNDO纠正了MNDO在R(•) + H-R'氢原子转移方面的严重错误，而对九个周环反应的活化势垒测试仅显示出适度的改善。
