化学键合模型概念的发展--从原子和分子轨道到化学轨道

Evolution of Concepts to Model Chemical Binding:From Atomic and Molecular Orbitals to Chemical Orbitals

对化学而言,对于连接分子中的原子的力的理论表达,历来一直是一个中心问题。要讨论此问题,就要预先在概念上对原子与分子有一个清楚的区分,而且要对原子的电子结构有一个适当的表达式。从历史上讲,对物质构成的研究,始于古希腊的德谟克利修斯,经过炼金术时代之后,由拉瓦锡、道尔顿、阿弗加德罗和门捷列夫的缓慢发展,成为了十八至十九世纪的化学。在上世纪初,出现了玻尔的原子理论和量子力学,它不仅标志着现代物理学的开始,而且也标志着量子化学的开始。原子轨道和分子轨道是海特勒-伦敦(HL)和原子轨道-分子轨道线性组合(LCAO-MO)方法中的基本概念,它导致了现代价键理论和哈特里-福克(HF)方法及其扩展方法的出现。电子计算机的发展带来了"计算化学",今天的计算机程序使得真正的结合能预测,甚至在没有使用经验参数的情况下,就成为现实。不过,用非半经验方法来对有合理尺寸和目前化学感兴趣的分子进行精确预测,常常需要惊人的计算量。把HF方法与HL算法合并的、现在称之为哈特里-福克-海特勒-伦敦(HF-HL)的方法,大大减少了在原子轨道或分子轨道从头计算模型中所需要的表达式的长度,这一简化使得对所形成的波函数容易得到解释。双原子分子HX和X2(X为H、He、Li、Be、B、C、N、O、F和Ne)的基态和少数激发态的计算是HF-HL方法的例子。进而,本文表明,HF-HL方法可以从带有一个新型轨道-化学轨道构建的简单波函数来导出,最后,对用化学轨道的初步计算进行了介绍。

For chemistry the theoretical representation of the forces connecting atoms in molecules was and is a central problem. Prerequisites are a clear conceptual distinction between atoms and molecules and an adequate representation of the electronic structure for atoms. Historically, the study on the constitution of matter starts in ancient Greece, likely with Democritus and slowly evolves after centuries of alchemy into the XVIII-XIX century chemistry, with Lavoisier, Dalton, Avogadro, and Mendeleyev. In the early years of last century, Bohr atomic theory and quantum mechanics did appear, marking the beginning not only of modem physics but and also of quantum chemistry. The Atomic Orbital and the Molecular Orbital are basic concepts in the Heitler-London, HL, and in the Linear Combination of Atomic Orbitals-Molecular Orbital, LCAO-MO, methods, which have lead to the modem Valence Bond and to the Hartree-Fock （and its extensions） methods. The advent of the electronic computers did bring about ＂computational chemistry＂： today computer programs allow realistic binding energies predictions even without the use of empirical parameters. However, accurate predictions from non semi-empirical methods often require enormous amount of computer power, if applied to molecules of reasonable size and current chemical interest. Merging of the Hartree-Fock with the Heitler-London algorithms, as recently proposed in the Hartree-Fock-Heitler-London, HF-HL, method drastically reduces the length of the expansions needed in AO or MO ab initio models. ; this simplification allows easy interpretation of the resulting wave function. The HF-HL method is exemplified with ground and a few excited states computations of diatomic molecules HX and X2 with X = H,He,Li, Be, B, C, N, O, F and Ne. Further, we show that the HF-HL method is derivable from a simple wave function constructed with a new type of orbitals, the Chemical Orbitals. Preliminary computations with Chemical Orbitals conclude this work.