monteswitch: A package for evaluating solid-solid free energy differences via lattice-switch Monte Carlo

Lattice-switch Monte Carlo (LSMC) is a method for evaluating the free energy between two given solid phases. LSMC is a general method, being applicable to a wide range of problems and interatomic potentials. Furthermore it is extremely efficient, ostensibly more efficient than other existing general methods.Here we introduce a package, monteswitch, which can be used to perform LSMC simulations. The package can be used to evaluate the free energy differences between pairs of solid phases, including multicomponent phases, via LSMC for atomic (i.e., non-molecular) systems in the NVT and NPT ensembles. It could also be used to evaluate the free energy cost associated with interfaces and defects. Regarding interatomic potentials, monteswitch currently supports various commonly-used pair potentials, including the hard-sphere, Lennard-Jones, and Morse potentials, as well as the embedded atom model. However the main strength of the package is its versatility: it is designed so that users can easily implement their own potentials.晶格切换蒙特卡洛（Lattice-switch Monte Carlo, LSMC）是一种用于计算两种给定固相之间自由能的方法。该方法属于通用框架，可应用于广泛的问题场景与原子间相互作用势。不仅如此，其效率极高，显著优于其他现有通用方法。本文介绍一款名为monteswitch的软件包，可用于开展LSMC模拟。该软件包可针对正则系综（NVT）与等压等温系综（NPT）下的非分子原子体系，通过LSMC方法计算各类固相（包括多组分固相）之间的自由能差。其还可用于评估与界面和缺陷相关的自由能代价。在原子间相互作用势方面，monteswitch目前支持多种常用对偶势，包括硬球势、伦纳德-琼斯（Lennard-Jones）势、莫尔斯（Morse）势以及嵌入原子模型（embedded atom model）。不过该软件包的核心优势在于其通用性：其设计允许用户轻松实现自定义的原子间相互作用势。