Aldossary Abdulrahman, Head-Gordon Martin
Pitzer Center for Theoretical Chemistry, Department of Chemistry, University of California, Berkeley, California 94720, USA.
J Chem Phys. 2022 Sep 7;157(9):094102. doi: 10.1063/5.0095443.
While bonding molecular orbitals exhibit constructive interference relative to atomic orbitals, antibonding orbitals show destructive interference. When full localization of occupied orbitals into bonds is possible, bonding and antibonding orbitals exist in 1:1 correspondence with each other. Antibonding orbitals play an important role in chemistry because they are frontier orbitals that determine orbital interactions, as well as much of the response of the bonding orbital to perturbations. In this work, we present an efficient method to construct antibonding orbitals by finding the orbital that yields the maximum opposite spin pair correlation amplitude in second order perturbation theory (AB2) and compare it with other techniques with increasing basis set size. We conclude the AB2 antibonding orbitals are a more robust alternative to the Sano orbitals as initial guesses for valence bond calculations due to having a useful basis set limit. The AB2 orbitals are also useful for efficiently constructing an active space, and they work as good initial guesses for valence excited states. In addition, when combined with the localized occupied orbitals, and relocalized, the result is a set of molecule-adapted minimal basis functions that is built without any reference to atomic orbitals of the free atom. As examples, they are applied to the population analysis of halogenated methane derivatives, H-Be-Cl, and SF, where they show some advantages relative to good alternative methods.
虽然成键分子轨道相对于原子轨道表现出相长干涉，但反键轨道表现出相消干涉。当占据轨道能够完全定域到键中时，成键轨道和反键轨道以1:1的对应关系存在。反键轨道在化学中起着重要作用，因为它们是决定轨道相互作用以及成键轨道对微扰响应的前沿轨道。在这项工作中，我们提出了一种有效的方法来构建反键轨道，即通过在二阶微扰理论（AB2）中找到产生最大相反自旋对相关振幅的轨道，并将其与随着基组大小增加的其他技术进行比较。我们得出结论，由于具有有用的基组极限，AB2反键轨道作为价键计算的初始猜测，是比佐野轨道更稳健的选择。AB2轨道对于有效地构建活性空间也很有用，并且它们作为价激发态的良好初始猜测。此外，当与定域占据轨道结合并重新定域时，结果是一组适应分子的最小基函数，其构建无需任何自由原子的原子轨道参考。作为示例，它们被应用于卤代甲烷衍生物、H-Be-Cl和SF的布居分析，在这些分析中它们相对于良好的替代方法显示出一些优势。
