Generating structures for further training

You have now seen the initial cross validation (CV) score using 10 initial training structures. We can further train the CE model using more training structures to make it more robust.

CLEASE supports 3 ways to generate more strucures. The first (and most obvious) is generating random structures as you have already done. The second method is to generate so called “probe structures” which differ the most from the existing training structures. The third method is to generate ground-state structures predicted based on current CE model.

Generate probe structures

You can generate probe structures using the following script. Note that it internally uses simulated annealing algorithm which uses fictitious temperature values to maximize the difference in correlation function of the new structure.

>>> from clease import NewStructures
>>> ns = NewStructures(settings, generation_number=1, struct_per_gen=10)
>>> ns.generate_probe_structure()

Once 10 additional structures are generated, you can re-run the script in “Running calculations on generated structures” section to calculate their energies. You should also run the script in “Evaluation of the CE model” section to evaluate the CV score of the model.It is likely that the CV score of the model is sufficiently low (few meV/atom or less) at this point.

Generate ground-state structures

You can now genereate ground-state structures to construct convex-hull plot of formation energy. The script below generates ground-state structures with a cell size of \(4 \times 4 \times 4\) at random compositions based on current CE model.

>>> from ase.db import connect
>>> import json
>>> # get template with the cell size = 4x4x4
>>> template = connect('aucu.db').get(id=17).toatoms()
>>> # import dictionary containing cluster names and their ECIs
>>> with open('eci_l1.json') as f:
...     eci = json.load(f)
>>> ns = NewStructures(settings, generation_number=2, struct_per_gen=10)
>>> ns.generate_gs_structure(atoms=template, init_temp=2000,
...                          final_temp=1, num_temp=10,
...                          num_steps_per_temp=5000,
...                          eci=eci, random_composition=True)

You should re-run the scripts in “Running calculations on generated structures” and “Evaluating the CE model” sections to see the convex-hull plot and the latest CV score of the model. If you observe that the CV score is high (more than ~5 meV/atom), you may want to repeat running the script for generating ground-state structures.