OCTP: A Tool for On-the-Fly Calculation of Transport Properties of Fluids with the Order‑n Algorithm in LAMMPS

We present a new plugin for LAMMPS
for on-the-fly computation of
transport properties (OCTP) in equilibrium molecular dynamics. OCTP
computes the self- and Maxwell–Stefan diffusivities, bulk and
shear viscosities, and thermal conductivities of pure fluids and mixtures
in a single simulation. OCTP is the first implementation in LAMMPS
that uses the Einstein relations combined with the order-n algorithm for the efficient sampling of dynamic variables. OCTP
has low computational requirements and is easy to use because it follows
the native input file format of LAMMPS. A tool for calculating the
radial distribution function (RDF) of the fluid beyond the cutoff
radius, while taking into account the system size effects, is also
part of the new plugin. The RDFs computed from OCTP are needed to
obtain the thermodynamic factor, which relates Maxwell–Stefan
and Fick diffusivities. To demonstrate the efficiency of the new plugin,
the transport properties of an equimolar mixture of water–methanol
were computed at 298 K and 1 bar.

本报告推出一款适用于 LAMMPS 的新型插件，旨在即时计算平衡分子动力学中的输运性质（OCTP）。OCTP 可计算纯净流体与混合物的自扩散率和 Maxwell-Stefan 扩散率、体积和剪切粘度，以及热导率。作为 LAMMPS 首次实现的 OCTP，采用 Einstein 关系与 order-n 算法相结合，高效地采样动态变量。OCTP 具有较低的计算需求，易于使用，因为它遵循 LAMMPS 的原生输入文件格式。新插件还包括一种计算超出截止半径的流体径向分布函数（RDF）的工具，同时考虑系统尺寸效应。从 OCTP 计算得到的 RDFs 可用于获取热力学因子，该因子关联 Maxwell-Stefan 扩散率和 Fick 扩散率。为了展示新插件的高效性，对水-甲醇等摩尔混合物的输运性质在 298 K 和 1 bar 条件下进行了计算。