Text Interface

The syntax of a FEASST text input file is follows. Each line begins with the name of a class in FEASST, listed below. The class name is then proceeded by space-separated pairs of argument names and values. Minor version changes support the same text files, but major version changes do not. For example, all text files for version v0.23.0 should also work with v0.23.1, but may not work with v0.24.0. For updating to a newer version, see the change log below.

Random Number Generators

These are the number generators available for use.


These classes describe the identity of the particles, their positions and the spatial domain in which they reside.

Nonbonded Isotropic Models

These classes include pair-wise (two-body) isotropic interactions models.

Nonbonded Potentials

These classes include various ways that interactions may be computed over a Selection or the entire Configuration.

Nonbonded Anisotropic Models

These classes include anisotropic interactions.

Long-Range Electrostatics

These classes include Ewald and long-range electrostatics.

Neighbor Lists

These classes store neighbors and their interaction energies.

One-Body Potentials

These classes include zero- and one-body interactions.

Bonded Interactions

The following bonded interactions are typically specified in fstprt files (see Particle files and units):

Thermodynamic Parameters

Acceptance Criteria

These classes determine if a MonteCarlo Trial is accepted or rejected.


These classes impose Constraints on the acceptance Criteria.

Monte Carlo Trials

These classes add Trials.


Analyze update/write every fixed number of trials, and do not change the simulation.


Modify update/write every fixed number of trials, but may change the simulation.


Actions happen once.

Flat Histogram

Flat-histogram simulations bias along a 1-dimensional macrostate.

Gibbs Ensemble

Simulate multiple configurations and transfer particles and/or volume between them.

Change Log

Below is a list of all notable changes made to the text interface which will likely lead to the errors if older text interface scripts use the newer version. Renamed arguments are shown as Class::old_argument->new_argument.

v0.24.6 to v0.25.0

  • Mie::n,m arguments replaced with mie_lambda_r,mie_lambda_a “Site Properties”

  • TablePotential base class VisitModel->Model

  • Trial::weight_per_number->weight_per_number_fraction

v0.23.1 to v0.24.0

  • Stepper::file_name->output_file

  • WriteModelParams::file_name->output_file

  • Checkpoint::file_name->checkpoint_file

  • GhostTrialGrow::trial_grow_file->grow_file

  • TrialGrowFile::file_name->grow_file

  • ReadConfigFromFile::file_name->input_file

  • ShapeFile::file_name->shape_file

  • ModelTableCart3DIntegr::file_name->table_file

  • ModelTableCart3DIntegr::shape_file_name->shape_file

The information available above is pruned from the C++ Interface documentation, with only the class arguments and no member functions. Therefore the C++ Interface documentation represents all capabilities of FEASST, many of which are hidden from text users for various reasons (e.g., because the classes may be used only internally, in development, buggy, depreciated or debugging tools).