多体展开方法中多体平滑函数以及中远程多体解析势能函数的设计

Many-body expansion (MBE) is the basis of many fragment-based methods for the computation of large molecular systems. It has many merits such as straightforward simple equations, naturally parallelized, and easy to implement. Its computation scaling is not linear if no cutoff is used to discard the computation of some many-body subsystems. However, if no delicate smooth functions were designed for the computation of the many-body correction energy, the potential energy surface computed would be discontinuous. In this project, we plan to design several generalized-switch functions to adaptively compute many-body correction energies. We also plan to design and optimize analytical potential energy functions (PEF) for medium-to-long range many-body interactions. Using the smooth functions we designed, we can seamlessly combine the high-level computation of many-body subsystems with short inter-fragment distances with the PEF computation of subsystems with medium-to-long inter-fragment distances. This scheme can effectively decrease the scaling of the computation of large molecular systems. We plan to design methods and programs based on MBE so that routinely computing large molecular systems by multilevel and multiscale methods becomes practical.

用于大分子体系的基于多体展开的分块计算方法具有简单，易于并行和程序化简单等特点。不过如果不采用截断舍弃一些多体的计算，其计算量并不是线性标度。但引入截断则需精心设计多体平滑函数，否则会导致势能面不连续，给构型优化和动力学模拟带来诸多严重问题。本项目拟设计普适的多体平滑函数，并对中远程多体相互作用拟合精确的解析势函数。利用多体平滑函数将近程多体的高精度从头算与中远程多体的解析势函数计算有机结合，从而实现大分子体系的线性标度计算，降低线性标度的斜率，并为实现大分子体系的第一性原理计算模拟开发切实可行的、基于多体展开的多水平、多尺度的计算方法和程序。

用于大分子体系的基于多体展开(MBE)的分块计算方法具有简单，易于并行和程序化简单等特点，但其计算量不是线性标度。本项目引入截断并为其精心设计普适多体平滑函数，解决了截断的多体展开分块算法其势能面不连续的问题，实现了大分子体系的线性标度计算，并降低了线性标度的斜率。本项目还开发了一款通用多体展开分块计算程序GSF-MBE，可以对体系进行自动分块，自动选取合适的计算水平，实现对复杂大分子体系的自动计算。本项目还在复杂体系的应用计算中取得了一系列重要成果。本项目共发表高水平SCI论文5篇。