pymatgen.analysis.piezo — pymatgen 2020.7.3 documentation

# Source code for pymatgen.analysis.piezo

    # coding: utf-8
    # Copyright (c) Pymatgen Development Team.
    # Distributed under the terms of the MIT License.

    """
    This module provides classes for the Piezoelectric tensor
    """
    from pymatgen.core.tensors import Tensor
    import numpy as np
    import warnings

    __author__ = "Shyam Dwaraknath"
    __copyright__ = "Copyright 2016, The Materials Project"
    __version__ = "1.0"
    __maintainer__ = "Shyam Dwaraknath"
    __email__ = "shyamd@lbl.gov"
    __status__ = "Development"
    __date__ = "Feb, 2016"

    class PiezoTensor(Tensor):
        """
        This class describes the 3x6 piezo tensor in Voigt-notation
        """

        def __new__(cls, input_array, tol=1e-3):
            """
            Create an PiezoTensor object.  The constructor throws an error if
            the shape of the input_matrix argument is not 3x3x3, i. e. in true
            tensor notation. Note that the constructor uses __new__ rather than
            __init__ according to the standard method of subclassing numpy
            ndarrays.

            Args:
                input_matrix (3x3x3 array-like): the 3x6 array-like
                    representing the piezo tensor
            """
            obj = super().__new__(cls, input_array, check_rank=3)
            if not (obj - np.transpose(obj, (0, 2, 1)) < tol).all():
                warnings.warn("Input piezo tensor does "
                              "not satisfy standard symmetries")
            return obj.view(cls)

        @classmethod
        def from_vasp_voigt(cls, input_vasp_array):
            """
            Args:
                input_vasp_array (nd.array): Voigt form of tensor.

            Returns:
                PiezoTensor
            """
            voigt_map = [(0, 0), (1, 1), (2, 2), (0, 1), (1, 2), (0, 2)]
            input_vasp_array = np.array(input_vasp_array)
            rank = 3

            pt = np.zeros([rank, 3, 3])
            for dim in range(rank):
                for pos in range(len(voigt_map)):
                    pt[dim][voigt_map[pos]] = input_vasp_array[dim][pos]
                    pt[dim].T[voigt_map[pos]] = input_vasp_array[dim][pos]

            return cls(pt)