【作者】 李伟；

【导师】 孙金锋；

【作者基本信息】 河南师范大学 ， 原子与分子物理， 2009， 硕士

【摘要】 分子势能函数是分子电子结构的完全描述。从势能函数不仅可以得到分子的能量、几何结构、力常量与光谱常数等性质,而且还可以为航天技术、激光技术、材料技术等许多高新技术领域的研究提供分子的光谱数据、结构参数等大量相关信息。因此,对分子精确势能函数的理论研究有着长期的实际需要,具有重要意义。由于双原子分子的势能仅是原子核间距的函数,因此双原子分子势能函数被认为是势能函数研究的基础问题。迄今该方面的多数研究主要集中在基态势能函数上。对于激发态,尤其是高激发态势能函数的研究却很少。本文在全面、系统介绍分子势能函数及相关量子化学计算方法的基础上,深入分析大量文献,并通过计算分析验证,探究了完全活性空间自洽场(CASSCF)方法的具体使用规律和较为详细的注意事项。随后,利用CASSCF方法对一些双原子分子的特殊势能函数进行了计算研究。首先,应用Gaussian03程序包中提供的完全活性空间自洽场(CASSCF)方法对BH分子基态( X ~1∑~+)与激发态( B ~1∑~+)的势能曲线进行了理论计算,不仅得到了这两个电子态的Murrell-Sorbie函数的解析表达式,而且利用该解析表达式进一步计算了这些电子态的光谱常数和力常量。为了验证计算结果的准确性和方法的可靠性,同时我们还利用对称匹配簇/对称匹配簇组态相互作用(SAC/SAC-CI)方法对以上两个电子态进行了理论计算。计算结果表明应用CASSCF方法得到的结果无论从计算时间还是结果的准确性上都比目前相对较好的理论计算结果(SAC/SAC-CI方法的计算结果)好。对BH分子激发态( B ~1∑~+)的势能曲线理论计算结果与实验结果之间的偏差进行了缜密地分析,发现光谱常数ω_eχ_e和α_e对势能曲线的形状有很大的影响。最终认为:实验光谱数据ω_eχ_e和α_e与理论计算结果相比较太小是造成偏差的主要原因。其次,利用CASSCF方法对OH分子第一激发态( A~2∑~+)的势能曲线进行了理论计算,并将计算结果拟合成解析的Murrell-Sorbie函数,进一步计算了该电子态相应的光谱数据,计算结果表明:对于开壳层分子,CASSCF方法依然可以给出比较好的结果。第三,分别应用CASSCF方法,M?Iler-Plesset微扰理论(MPPT)方法,密度泛函理论(DFT)方法对CuIn分子当前极存在争议的基态势能函数进行了理论计算。结果显示,MP2方法得到的结果与CASSCF方法和DFT方法得到的结果不一致。应用CASSCF方法和DFT方法得到的CuIn分子基态在完全离解之前势能函数上不存在极大值,而由MP2方法得到的结果恰恰相反(势能函数上存在一个极大值)。对此本文也做出了具体分析。更多还原

【Abstract】 Potential energy function is the complete description of electronic structure for molecule itself. Not only the molecular energy, geometrical configuration, force constant, spectroscopic constant are obtained from potential energy function, but it also provides a lot of information for the investigation in the high and new-technology field. For instance, spaceflight, laser, material, and so on. Therefore, it is necessary to accurately investigate the molecular potential energy function from theoretical level. The potential energy function of the diatomic molecule is considered as the basic issues. Because of, it is only the function of the internuclear distance. To date, the major researches in this field mainly are concentrated in the ground state. For the excited state, especially the high-excited state potential energy function, the researches are few.Based on a comprehensive and systematic introduction of molecular potential energy function and correlative quantum chemical methods and a lot of documents, Complete Active Space Self-Consistent Field (CASSCF) method is explored. Then, the investigations on the irregular potential energy curves of the diatomic molecule are calculated by means of CASSCF method. Firstly, with the CASSCF method, provided by the Gaussian03 program package, the potential energy curves for the electronic states X~1∑~+and B~1∑~+of BH molecule are calculated respectively. Not only the analytical form of Murrell-Sorbie function is obtained, but the spectroscopic constant and force constant are also calculated depending on this analytical function. In order to prove the accuracy of the computational results and the reliability of the CASSCF method, Symmetry Adapted Cluster/Symmetry Adapted Cluster Configuration Interaction (SAC/SAC-CI) is used to calculate the two electronic states mentioned above. The results show that the CASSCF result is more accurate than the SAC/SAC-CI, which is considered as a better method. Simultaneously, the deviation between the CASSCF result and experimental data of the B 1∑+electronic state potential energy curve is analyzed rigorously. It shows the shape of the potential curve is affected byω_eχ_e andα_e intensely. So, we believe this mainly dues to the fact that the experimental spectroscopic dataω_eχ_e andα_e are too similar to the theoretical result. Secondly, the potential energy curve of A~2∑~+electronic state for OH molecule is calculated with CASSCF method. Then, fit the computational result into the Murrell-Sorbie function. The spectroscopic data of this electronic state is calculated furtherly. This result shows that, for the open shell molecule, the better result can also be gotten with the CASSCF method. Thirdly, the ground state potential energy curve of the CuIn molecule, which is very controversial, is respectively calculated via the CASSCF method, MP2 method, DFT method. The results show that MP2 result is different from the CASSCF and DFT. The CASSCF result and the DFT result suggest that the potential energy curve of the ground state for the CuIn molecule is a regular curve. However, from the MP2 result, we can see that there exists a maximum on the potential energy curve before dissociation limit. We also give some analyses in this paper.更多还原