SYMM :

This is an alternative to the GROUp command. The SYMM keyword should be followed by three lines containing the rotational and translational part of a valid symmetry operator as shown below for the operator 1/2 - x, 1/2 + y,$\bar{z}$

                      SYMM
                       -1.0  0.0  0.0       0.50
                        0.0  1.0  0.0       0.50
                        0.0  0.0 -1.0       0.00

The identity operator is defined internally and should not be given. QS does not understand fractions, so translational parts like 1/6 must be converted to floats with a sufficient number of decimal digits after the period (0.33 will be converted by QS to 0.3300 which for most problems is a bad approximation to 1/3. You are better off giving something like 0.33333333).