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.格点切换蒙特卡洛方法（Lattice-switch Monte Carlo，缩写LSMC）是一种用于评估两种给定固相之间自由能的方法。作为一款通用方法，它可适用于广泛的问题类型与原子间势函数。此外，该方法具备极高的计算效率，直观上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。该软件包能够针对正则系综（NVT ensemble）与等温等压系综（NPT ensemble）下的原子（即非分子）体系，通过LSMC方法计算包括多组分相在内的各成对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。在原子间势函数方面，monteswitch目前支持多种常用的对势，包括硬球势、伦纳德-琼斯势（Lennard-Jones potential）、莫尔斯势（Morse potential）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：其设计使得用户可以轻松实现自定义的势函数。