The forcefield directory is a place for files which describe atoms, molecules and coarse-grained models.

Data files

Files which begin with the name “data” are LAMMPS-inspired data files.

They deviate from LAMMPS data files as follows:

Nomenclature and style

  • atoms in LAMMPS are analogous to sites in FEASST.

  • molecules in LAMMPS are analogous to particles in FEASST.

  • FEASST data files may only contain one particle.

  • all FEASST indices (types, sites, etc) begin with 0, not 1.

  • characters are case sensitive

  • the number of spaces between characters does not matter

  • LMP Coeffs sections were replaced by Properties sections, with different formatting

  • “2 dimensions” may be specified at the beginning of the file for a 2D simulation.

Site Properties

This is where the biggest difference from the LAMMPS data format is present. Each site type may have a list of properties given by a label and value.

The format for this section is as follows:

[site index] [label_0] [value_0] … [label_n] [value_n]


Charge is a site-type property, and thus is not included for each site. In addition, wrapping is also not included.

The format for this section is as follows:

[site index] [site type] [x-position] [y-position] [z-position]

Site Labels

Site labels are used to attach a name to the site type, often used for visualization programs, etc. Note: these are not currently implemented.