A small error in the example.

[sxm13]

For the LJ parameter of N2 in the force_field.json,

{ "name" : "N_n2", "type" : "lennard-jones",
"parameters" : [38.298, 3.306], "source" : "A. Martin-Calvo et al. , Phys. Chem. Chem. Phys. 2011, 13, 11165-11174" }, { "name" : "_Nn2", "type" : "none",
"parameters" : [0.0, 1.0], "source" : "A. Martin-Calvo et al. , Phys. Chem. Chem. Phys. 2011, 13, 11165-11174" }

maybe should change to

{ "name" : "N_n2", "type" : "lennard-jones",
"parameters" : [38.298, 3.306], "source" : "A. Martin-Calvo et al. , Phys. Chem. Chem. Phys. 2011, 13, 11165-11174" }, { "name" : "_Ncom", "type" : "none",
"parameters" : [0.0, 1.0], "source" : "A. Martin-Calvo et al. , Phys. Chem. Chem. Phys. 2011, 13, 11165-11174" }

[dubbelda]

Thanks, fixed!