LAMMPS lb/fluid fix version 2: Improved hydrodynamic forces implemented into LAMMPS through a lattice-Boltzmann fluid

The first version of this code (Mackay et al., 2013) [10] implemented long-range hydrodynamic interactions into the open-source molecular dynamics package LAMMPS. This was done through the creation of a fix, lb/fluid which was subsequently included as a user-package in the main LAMMPS distribution. Here we substantially update this package by making improvements to its accuracy, adding significant new features, and by simplifying the use of the package. A new two-pass interpolation and spreading scheme is introduced which results in the improved accuracy and numerical stability. New features include new output options, several added computes, and mesh geometry option suitable for micro- and nano-fluidic device simulations. The original package could require fairly careful calibration to obtain accurate thermostating and accurate reproduction of properties related to the hydrodynamic size of objects such as colloids. This process has now been largely automated so that the default settings should suffice for most applications.