σπ model in the atom-bond electronegativity equalization method and its applications

Based on density functional theory and electronegativity equalization principle, a an model, which considers the structure of double bond for the first timet is developed, In this model the double bond is partitioned into one sigma bond region and four pi bond regions. The atom-bond electronegativity equalization method plus sigma pi model(ABEEM sigma pi) is then proposed for the calculation of charge distribution and charge polarization in large molecules. It has been shown that the results of charge distribution in large molecules obtained by ABEEM sigma pi model agree with those obtained by ab initio method very well. In addition, the model can be used to explain the region-selectivity of Diels-Alder reaction successfully. All these indicate that ABEEM sigma pi model is reasonable and reliable.