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)