利用分子相似性建立精确的半经验电子结构理论
Using molecular similarity to construct accurate semiempirical electron structure theories
摘要：
从头算电子结构方法对小系统给出了精确的结果，但不能很好地扩展到大系统。化学洞察力告诉我们，分子官能团在所有分子中的行为大致相同，无论大小。这种分子的相似性被利用在半经验方法中，该方法将简单的电子结构理论与官能团的可转移特性参数相结合。我们提出，高层次的小分子计算提供了丰富的参数化数据来源。原则上，我们可以选择一个官能团，在各种小分子环境中生成大量关于该基团的从头算数据，并“挖掘”这些数据，为该基团在大分子中的行为建立一个复杂的模型。这项工作详细介绍了这样一个模型的电子相关性：一个半经验的，基于子系统的相关功能，预测一个子系统的双电子密度作为其单电子密度的功能。这个模型证明了两个小的系统：线性，最小的基础（H-H）5链，作为一个总和的四个重叠（H-H）2子系统;和一组HOC-R分子的醛基。结果初步证明了这种方法的可行性。
英文摘要：
Ab initio electronic structure methods give accurate results for small systems, but do not scale well to large systems. Chemical insight tells us that molecular functional groups will behave approximately the same way in all molecules, large or small. This molecular similarity is exploited in semiempirical methods, which couple simple electronic structure theories with parameters for the transferable characteristics of functional groups. We propse that high-level calculations on small molecules provide a rich source of parametrization data. In principle, we can select a functional group, generate a large amount of ab initio data on the group in various small-molecule environments, and "mine" this data to build a sophisticated model for the group's behavior in large molecules. This work details such a model for electron correlation: a semiempirical, subsystem-based correlation functional that predicts a subsystem's two-electron density as a functional of its one-electron density. This model is demonstrated on two small systems: chains of linear, minimal-basis (H-H)5, treated as a sum of four overlapping (H-H)2 subsystems; and the aldehyde group of a set of HOC-R molecules. The results provide an initial demonstration of the feasibility of this approach.
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