# calc_elastic_constants_static.py

## Calculation script functions

elastic_constants_static(lammps_command, system, potential, mpi_command=None, strainrange=1e-06, etol=0.0, ftol=0.0, maxiter=10000, maxeval=100000, dmax=0.01)

Repeatedly runs the ELASTIC example distributed with LAMMPS until box dimensions converge within a tolerance.

Parameters
• lammps_command (str) – Command for running LAMMPS.

• system (atomman.System) – The system to perform the calculation on.

• potential (atomman.lammps.Potential) – The LAMMPS implemented potential to use.

• mpi_command (str, optional) – The MPI command for running LAMMPS in parallel. If not given, LAMMPS will run serially.

• strainrange (float, optional) – The small strain value to apply when calculating the elastic constants (default is 1e-6).

• etol (float, optional) – The energy tolerance for the structure minimization. This value is unitless. (Default is 0.0).

• ftol (float, optional) – The force tolerance for the structure minimization. This value is in units of force. (Default is 0.0).

• maxiter (int, optional) – The maximum number of minimization iterations to use (default is 10000).

• maxeval (int, optional) – The maximum number of minimization evaluations to use (default is 100000).

• dmax (float, optional) – The maximum distance in length units that any atom is allowed to relax in any direction during a single minimization iteration (default is 0.01 Angstroms).

Returns

Dictionary of results consisting of keys:

• ’a_lat’ (float) - The relaxed a lattice constant.

• ’b_lat’ (float) - The relaxed b lattice constant.

• ’c_lat’ (float) - The relaxed c lattice constant.

• ’alpha_lat’ (float) - The alpha lattice angle.

• ’beta_lat’ (float) - The beta lattice angle.

• ’gamma_lat’ (float) - The gamma lattice angle.

• ’E_coh’ (float) - The cohesive energy of the relaxed system.

• ’stress’ (numpy.array) - The measured stress state of the relaxed system.

• ’C_elastic’ (atomman.ElasticConstants) - The relaxed system’s elastic constants.

• ’system_relaxed’ (atomman.System) - The relaxed system.

Return type

dict

main(*args)

Main function called when script is executed directly.

process_input(input_dict, UUID=None, build=True)

Processes str input parameters, assigns default values if needed, and generates new, more complex terms as used by the calculation.

Parameters
• input_dict (dict) – Dictionary containing the calculation input parameters with string values. The allowed keys depends on the calculation style.

• UUID (str, optional) – Unique identifier to use for the calculation instance. If not given and a ‘UUID’ key is not in input_dict, then a random UUID4 hash tag will be assigned.

• build (bool, optional) – Indicates if all complex terms are to be built. A value of False allows for default values to be assigned even if some inputs required by the calculation are incomplete. (Default is True.)