Is PLUMED free?
Yes, it is free and licensed under the Lesser GNU General Public License. We only ask you to cite the following references in any work you publish using PLUMED:
If you used PLUMED 2.x
G.A. Tribello, M. Bonomi, D. Branduardi, C. Camilloni, G. Bussi, PLUMED2: New feathers for an old bird, Comp. Phys. Comm. 185, 604 (2014)
Available also on arXiv:1310.0980
If you used PLUMED 1.x