@staticmethod
def parse_line(line):
    """
        Parse line inputs.

        **Parameters**

            line: *str*
                A string that holds a three-body Morse parameter set.

        **Returns**

            indices: *tuple, str*
                The labels in the line corresponding to atom types.
            D0: *float*
                The depth of the potential well.
            alpha: *float*
                The width of the potential well.
            r0: *float*
                The interatomic distance associated with the minimum.
            rc: *float*
                The cutoff of the potential.
        """
    line = line.strip().split()
    assert len(line) in [5, 6], 'Error - Invalid line to parse!'
    indices = line[0], line[1]
    D0 = float(line[2])
    alpha = float(line[3])
    r0 = float(line[4])
    rc = None
    if len(line) == 6:
        rc = float(line[5])
    return indices, D0, alpha, r0, rc
