【摘要】 采用传统的Hartree-Fock（HF）从头算和密度泛函中的B3LYP和B3PW91方法,选择了不同基组水平（STO-3G,3-21G和6-31G^*）对卟吩结构进行了全几何优化,并对得到的结果相互进行了比较,同时与实验数据进行了对照。结果表明,对于H₂P以及具有类似结构的卟啉衍生物,传统的HF方法得到的几何构型以及相关性质（核磁共振谱,NMR）并不可靠。这种体系中电子相关能是不可忽略的。在B3LYP水平上选用较小的基组3-21G得到的结果与中等基组6-31G^*差别不大,但是最小基组STO-3G得到的优化构型却是一个鞍点结构。更多还原

【Abstract】 The molecular structure of Free-Base Porphyrin（H₂P）has been fully optimized using the Density Functional Theory（DFT） B3LYP and B3PW91 methods,as well as ab initio Hartree-Fock method.Various basis sets STO-3G,3-21G and 6-31G^* have been employed.The results obtained at various levels are discussed and compared with each uther and with the available experimental data. It was shown that calculations performed at the Hartree-Fock level cannot produce a reliable geometry and related properties such as the Nuclear Magnetic Resonance（NMR）of H₂P and similar porphyrin-based systems.Electron correlation must be included in the calcu- lations.The basis set has comparatively less effect on the calculated results.The results derived at the B3LYP level using the smaller 3-21G basis set were very close to those produced using the medium 6-31G^* basis set.However,the optimized structure obtained from the smallest basis set,STO-3G,was a saddle type.更多还原