Parses boltztrap.struct file (only the volume)
        Args:
            path_dir: (str) dir containing the boltztrap.struct file

        Returns:
            (float) volume

def parse_struct(path_dir):
        """
        Parses boltztrap.struct file (only the volume)
        Args:
            path_dir: (str) dir containing the boltztrap.struct file

        Returns:
            (float) volume
        """
        with open(os.path.join(path_dir, "boltztrap.struct"), 'r') as f:
            tokens = f.readlines()
            return Lattice([[Length(float(tokens[i].split()[j]), "bohr").
                           to("ang") for j in range(3)] for i in
                            range(1, 4)]).volume