论文部分内容阅读
通过对 BH、 AlH、 BF和 AlF的高级别 ab initio势能曲线计算和理论分析 ,发现在分子的几何构型偏离平衡时 ,由于参考态组态不充分的问题 ,Hartree-Fock单参考态的 MPn微扰计算可能给出错误的能量值 .从而表明，目前的精确模型化学方法 (G1、 G2、 G3和 CBS系列 )中用 MPn微扰外推的办法拟合高级别 ab initio,对偏离平衡构型体系 (如动力学研究中的过渡态、中间体等 )的能量计算 ,在一般意义上是不可靠的 .但是 ,在相同的参考态上 ,即使 MPn微扰能已经发生错误 ,QCISD(T)、 CCSD(T)方法却能较好地描述分子解离过程的能量 ,且 QCISD(T)比 CCSD(T)更好 .因此 ,在单参考态理论框架内，发展以严格的 QCISD(T)方法为基础的模型化学方法 ,似更适用于反应动力学方面的研究 .
Through the calculation and theoretical analysis of high-level ab initio potential curves of BH, AlH, BF and AlF, it was found that due to the inadequate configuration of the reference state, when the geometrical configuration of the molecule deviates from equilibrium, the Hartree-Fock single reference state MPn Perturbation calculations may give incorrect energy values, thus indicating that the current method of accurate model chemistry (G1, G2, G3, and CBS series) extrapolates MPn perturbations to high-level ab initio, The energy calculations of type systems (eg, transition states, intermediates, etc. in kinetic studies) are not generally reliable. However, even in the same reference state, even if errors have occurred in MPn perturbation energy, QCISD (T (T) is better than that of CCSD (T). Therefore, in the framework of single reference state theory, we develop a rigorous QCISD (T) method which can describe the energy of the molecular dissociation process well, ) Method-based model chemistry method, it seems more suitable for the study of reaction kinetics.