The files in this directory are a user-contributed package for LAMMPS. The person who created these files is Axel Kohlmeyer (akohlmey@cmm.chem.upenn.edu). Contact him directly if you have questions or for example scripts that use it. This package implements a "fix smd" command which can be used in a LAMMPS input script. SMD stands for steered molecular dynamics. Here is what Axel said about the new fix: Please find attached a fix that I was asked to write for our "coarse-grainers". They need free energy profiles for their parametrization and this seems to work best. The code basically is a version of "fix spring" on steroids (constant velocity pulling with velocity set to zero should recover "fix spring"), but I found it cleaner to have it in a seprarate class since otherwise the result may become too convoluted for people that only want to use "fix spring".