@staticmethod
def get_elastic_constants(filename='OUTCAR', lines=None):
    lines = _get_lines_from_file(filename=filename, lines=lines)
    trigger_indices = _get_trigger(lines=lines, filename=filename, trigger='TOTAL ELASTIC MODULI (kBar)', return_lines=False)
    if (len(trigger_indices) != 1):
        return None
    else:
        start_index = (trigger_indices[0] + 3)
        end_index = (start_index + 6)
        elastic_constants = []
        for line in lines[start_index:end_index]:
            elastic_constants.append(line.split()[1:])
        elastic_GPa = (np.array(elastic_constants, dtype=float) / 10)
        return elastic_GPa
@staticmethod
def get_elastic_constants(filename='OUTCAR', lines=None):
    lines = _get_lines_from_file(filename=filename, lines=lines)
    trigger_indices = _get_trigger(lines=lines, filename=filename, trigger='TOTAL ELASTIC MODULI (kBar)', return_lines=False)
    if (len(trigger_indices) != 1):
        return None
    else:
        start_index = (trigger_indices[0] + 3)
        end_index = (start_index + 6)
        elastic_constants = []
        for line in lines[start_index:end_index]:
            elastic_constants.append(line.split()[1:])
        elastic_GPa = (np.array(elastic_constants, dtype=float) / 10)
        return elastic_GPa