Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, USA.
J Chem Phys. 2019 Nov 7;151(17):170901. doi: 10.1063/1.5126216.
Since the introduction of the fragment molecular orbital method 20 years ago, fragment-based approaches have occupied a small but growing niche in quantum chemistry. These methods decompose a large molecular system into subsystems small enough to be amenable to electronic structure calculations, following which the subsystem information is reassembled in order to approximate an otherwise intractable supersystem calculation. Fragmentation sidesteps the steep rise (with respect to system size) in the cost of ab initio calculations, replacing it with a distributed cost across numerous computer processors. Such methods are attractive, in part, because they are easily parallelizable and therefore readily amenable to exascale computing. As such, there has been hope that distributed computing might offer the proverbial "free lunch" in quantum chemistry, with the entrée being high-level calculations on very large systems. While fragment-based quantum chemistry can count many success stories, there also exists a seedy underbelly of rarely acknowledged problems. As these methods begin to mature, it is time to have a serious conversation about what they can and cannot be expected to accomplish in the near future. Both successes and challenges are highlighted in this Perspective.
自 20 年前引入碎分子轨道方法以来，基于片段的方法在量子化学中占据了一个虽小但不断增长的利基市场。这些方法将一个大的分子系统分解成足够小的子系统，以便进行电子结构计算，然后重新组装子系统信息，以近似否则难以处理的超系统计算。碎片回避了从头计算成本的急剧上升（相对于系统大小），取而代之的是分布在众多计算机处理器上的成本。这些方法之所以具有吸引力，部分原因是它们易于并行化，因此很容易适应百亿亿次级计算。因此，人们曾希望分布式计算可能会为量子化学提供所谓的“免费午餐”，而入口是对非常大的系统进行高级计算。虽然基于片段的量子化学有许多成功的案例，但也存在一些鲜为人知的问题。随着这些方法开始成熟，是时候就它们在不久的将来能够完成和不能完成的任务进行认真的讨论了。本文重点介绍了这些方法的成功和挑战。
