hysteresis.py generates a hysteresis loop of a ferroelectric material according to Garrity et al 2014.
Requires Numpy, Scipy, Matplotlib, PyYAML.
To generate hysteresis loop, first, create YAML file with values for
cell_dims: dimensions of unit cell in bohr.energy_data: path to text file containing space-delimited table. Column 1 contains values of effective coordinate Q (normalised between -1 and 1) expressing an atomic configuration in a 3N-dimensional space between the 2 relaxed ferroelectric configurations. Column 2 contains corresponding values of the energy per unit cell in hartrees.chi_data: path to text file containing space-delimited table. Column 1 contains values of effective coordinate Q (normalised between -1 and 1) expressing an atomic configuration in a 3N-dimensional space between the 2 relaxed ferroelectric configurations. Column 2 contains corresponding values of the electronic contribution to the linear polarizability (in cgs units).remnant_polarisation: remnant polarisation of ferroelectric in uC/cm2.Emax: maximum external field at which to calculate equilibrium polarization in kV/cm.Esamples: number of electric field values between -Emax and +Emax at which polarization will be calculated.debug: int indicating whether contributions to free energy should be printed during minimizations.- 0: never output;
- 1: output after minimization;
- 2: output at each free energy evaluation during minimization.
See ferro_scripts/example_params.yaml for an example.
Then cd into the ferro_scripts directory and run
python hysteresis.py <path to params YAML file>.
Troubleshooting
- Hysteresis loop contains fewer points than expected. The electric field values specified through
EmaxandEsamplesmay be too large, which leads to most free energy curves having minima outside$Q\in[-1,1]$ . Try reducingEmaxand/or increasingEsamples.