Source code for mchammer.observers.constituent_strain_observer

from mchammer.observers.base_observer import BaseObserver
from icet.tools import ConstituentStrain
from ase import Atoms




class ConstituentStrainObserver(BaseObserver):
    """
    This class represents a constituent strain observer.

    It records the constituent strain energy of the configuration separately
    from the energy the cluster expansion describes, which is useful in a
    simulation with a :class:`ConstituentStrainCalculator
    <mchammer.calculators.ConstituentStrainCalculator>`, where the potential
    stored in the data container is the sum of the two.
    The value is stored in the data container under the key
    ``constituent_strain_energy`` and refers to the whole supercell.
    The section on :ref:`constituent strain <constituent_strain_example>` shows
    the observer in use.

    The observer reads the structure factors the :class:`ConstituentStrain
    <icet.tools.ConstituentStrain>` object holds but does not move them.
    It can therefore share the object with the calculator that samples the
    same configuration.

    Parameters
    ----------
    constituent_strain
        Object that defines the strain energy of the system.
        Its supercell has to be the one the simulation samples.
    interval
        Observation interval in trial steps.
        By default the ensemble the observer is attached to sets the interval
        to the number of sites in the structure.
    """

    def __init__(self,
                 constituent_strain: ConstituentStrain,
                 interval: int | None = None) -> None:
        super().__init__(interval=interval, return_type=dict, tag='ConstituentStrainObserver')
        self.constituent_strain = constituent_strain



    def get_observable(self, structure: Atoms) -> dict:
        """
        Returns the constituent strain energy of a configuration.

        Parameters
        ----------
        structure
            Atomic configuration to observe.

        Returns
        -------
        dict
            The constituent strain energy of the whole supercell under the key
            ``constituent_strain_energy``.
        """
        # Observing must not move the structure factors, which a calculator
        # sampling the same ConstituentStrain object reads as the value
        # before the next change.
        cs = self.constituent_strain.get_constituent_strain(
            structure.get_atomic_numbers(), update_structure_factors=False)
        cs = {'constituent_strain_energy': cs * len(structure)}
        return cs