Scalable electronic structure theory: the embedded electron-pair approximation

量子力学理论提供了计算分子结构和分子行为的方法。计算很复杂，部分原因是一个分子有许多相互作用的成分，部分原因是量子力学本身固有的复杂性。对于最简单的系统，可以得到精确的量子力学结果，但对于实际问题，需要近似。产生这些近似，然后将它们转化为有用的软件工具的领域是分子电子结构理论。事实证明，被引用最多的化学论文描述了分子电子结构理论的突破。原因是这些方法可以普遍适用：它们可以告诉我们任何分子的结构和反应性，因此它们被广泛的化学家使用。目前，在该领域占主导地位的两种近似：密度泛函理论(DFT)和耦合团簇理论(CC)。第一个是非常高效的(在计算机上运行很快)，第二个对于许多问题来说是惊人的准确。在使DFT更准确和CC理论更有效方面已经有了很大的进展；我们的团队已经参与了其中的一些努力。在这个建议中，我们提出了分子电子结构理论的一个新分支，基于一次处理一个电子对的概念，但每对电子嵌入到一个由分子其余部分提供的模型中。这些方法可能是革命性的，因为它们的成本似乎并不比DFT高出多少，但它们的精度可能与CC理论相媲美。现在是这项研究的合适时机，部分是因为对更好的理论方法的需求；部分是因为最近量子嵌入理论的突破为建立新的、可能令人惊叹的电子结构方法提供了一个非凡的机会。

The theory of quantum mechanics provides the means to calculate the structure of molecules, and how molecules will behave. The calculations are complicated, partly because a molecule has many interacting components, and partly because of the intrinsic complications of quantum mechanics itself. Exact quantum mechanical results can be obtained for the simplest of systems, but for real problems, approximations are needed. The field that produces these approximations, then converts them into usable software tools is molecular electronic structure theory.It turns out that the most highly cited papers in chemistry describe breakthroughs in molecular electronic structure theory. The reason is that these methods can be applied universally: they can inform us about the structure and reactivity of any molecule, so they are used by an enormous range of chemists.Currently two approximations dominate the field, density functional theory (DFT) and coupled cluster theory (CC). The first is very efficient (ie runs quickly on computers) and the second is amazingly accurate for many problems. There has been a great deal of progress in making DFT more accurate, and CC theory more efficient; our group has been involved in some of these efforts.In this proposal we set out a new branch of molecular electronic structure theory, based on the concept of treating the electrons one pair at a time, but with each pair embedded in a model provided by the rest of the molecule. These methods could be revolutionary, because their cost appears not much greater than that of DFT, but their accuracy could be competitive with CC theory. Now is the right time for this research partly because of the demand for better theoretical methods; and partly because recent breakthroughs in quantum embedding theory give a remarkable opportunity to build new and potentially amazing electronic structure methods.