Texas A&M University at Galveston, P.O. Box 1675, Galveston, Texas 77553, USA.
J Chem Phys. 2011 Nov 21;135(19):194103. doi: 10.1063/1.3659294.
The Hubbard model, which is widely used in physics but is mostly unfamiliar to chemists, provides an attractive yet simple model for chemistry beyond the self consistent field molecular orbital approximation. The Hubbard model adds an effective electron-electron repulsion when two electrons occupy the same atomic orbital to the familiar Hückel Hamiltonian. Thus it breaks the degeneracy between excited singlet and triplet states and allows an explicit treatment of electron correlation. We show how to evaluate the parameters of the model from high-level ab initio calculations on two-atom fragments and then to transfer the parameters to large molecules and polymers where accurate ab initio calculations are difficult or impossible. The recently developed MS-RASPT2 method is used to generate accurate potential energy curves for ethene as a function of carbon-carbon bond length, which are used to parameterize the model for conjugated hydrocarbons. Test applications to several conjugated/aromatic molecules show that even though the model is very simple, it is capable of reasonably accurate predictions for bond lengths, and predicts molecular excitation energies in reasonable agreement with those from the MS-RASPT2 method.
哈伯德模型在物理学中被广泛应用，但化学界对此知之甚少，它为超越自洽场分子轨道近似的化学提供了一个有吸引力但简单的模型。哈伯德模型在熟悉的休克尔哈密顿量中添加了一个有效电子-电子排斥项，当两个电子占据相同的原子轨道时。因此，它打破了激发单线态和三线态之间的简并，并允许对电子相关进行显式处理。我们展示了如何从两个原子片段的高精度从头算计算中评估模型的参数，然后将参数转移到大分子和聚合物中，在这些体系中，精确的从头算计算是困难或不可能的。最近开发的 MS-RASPT2 方法用于生成乙烯作为碳-碳键长函数的精确势能曲线，这些曲线用于为共轭碳氢化合物参数化模型。对几个共轭/芳香族分子的测试应用表明，尽管该模型非常简单，但它能够对键长进行相当准确的预测，并预测分子激发能与 MS-RASPT2 方法的预测相当吻合。
