@molecs = (
    dir_tree( 'AB', 6, 1, 1 ),
    dir_tree( 'BC', 6, 1, 1 ),
   # dir_tree( 'XZ', 6, 1, 4 ),
   # dir_tree( 'XY', 6, 1, 4 ),
   # dir_tree( 'QU', 6, 1, 4 ),
   # dir_tree( 'QE', 6, 1, 4 ),
);