# Source code for mchammer.calculators.constituent_strain_calculator

```
from icet.tools import ConstituentStrain
from icet import ClusterExpansion
from mchammer.calculators import ClusterExpansionCalculator
from typing import List, Union
import numpy as np
[docs]class ConstituentStrainCalculator(ClusterExpansionCalculator):
"""
Calculator for handling cluster expansions with strain.
Parameters
----------
constituent_strain
ConstituentStrain object defining the strain energy
properties of the system; the supercell used to
create this object should corresponding to the one
used when running Monte Carlo simulations with this
calculator
cluster_expansion
cluster expansion from which to build ClusterExpansionCalculator
name
human-readable identifier for this calculator
scaling
scaling factor applied to the property value predicted by the
cluster expansion
"""
def __init__(self, constituent_strain: ConstituentStrain,
cluster_expansion: ClusterExpansion,
name: str = 'Constituent Strain Calculator',
scaling: Union[float, int] = None):
self.constituent_strain = constituent_strain
super().__init__(structure=constituent_strain.supercell,
cluster_expansion=cluster_expansion,
name=name,
scaling=scaling)
[docs] def calculate_total(self, *, occupations: np.ndarray) -> float:
"""
Calculates and returns the total property value of the current
configuration.
Parameters
----------
occupations
the entire occupation vector (i.e. an array of atomic numbers as integers)
"""
e = super().calculate_total(occupations=occupations)
e += len(occupations) * \
self.constituent_strain.get_constituent_strain(occupations)
return e
[docs] def calculate_change(self, *, sites: List[int],
current_occupations: List[int],
new_site_occupations: List[int]) -> float:
"""
Calculates and returns the sum of the contributions to the property
due to the sites specified in `local_indices`
Parameters
----------
sites
index of sites at which occupations will be changed
current_occupations
entire occupation vector (atomic numbers) before change
new_site_occupations
atomic numbers after change at the sites defined by `sites`
"""
if len(new_site_occupations) > 1:
raise NotImplementedError('Only single flips are currently allowed in '
'conjunction with the constituent strain calculator.')
e = super().calculate_change(sites=sites,
current_occupations=current_occupations,
new_site_occupations=new_site_occupations)
de_cs = self.constituent_strain.get_constituent_strain_change(current_occupations,
sites[0])
e += len(current_occupations) * de_cs
return e
[docs] def accept_change(self):
"""
Informs the ConstituentStrain object that the most
recent change was accepted, such that the new
structure factor can be stored.
"""
self.constituent_strain.accept_change()
```