[Wien] Can w2web see symmetry?

[John Rundgren]

The following case.struct file shows a UC for a surface slab (a periodic
repetition of atoms and gap i the z direction). The UC contains 9 atomic
layers; it has sgroup 157 P31m with 6 xy symmetries.

The slab is designed with a z mirror symmetry as is shown by XCrySden.
Actually UC fulfills sgroup 189 P-62m with 12 symmetries. I know by
accident in this particular case.

Does w2web not always detect the complete symmetry of a given
case.struct? A question about speed of calculation.

Is there a general rule for extending sgroup A with N xy symmetries to
sgroup B with N xy symmetries + 1 z mirror? A question typic of surface
physics.

Best regards, John Rundgren

Cl-Ru0001
H   LATTICE,NONEQUIV.ATOMS   9  157 P31m    
MODE OF CALC=RELA unit=bohr
  8.856390  8.856390 59.832509 90.000000 90.000000120.000000
ATOM  -1: X=0.00000000 Y=0.00000000 Z=0.26312000
          MULT= 1          ISPLIT=15
Cl         NPT=  781  R0=.000100000 RMT=   2.15000   Z:  17.00000
LOCAL ROT MATRIX:    1.0000000 0.0000000 0.0000000
                     0.0000000 1.0000000 0.0000000
                     0.0000000 0.0000000 1.0000000
ATOM  -2: X=0.32907000 Y=0.00000000 Z=0.20202000
          MULT= 3          ISPLIT=15
      -2: X=0.00000000 Y=0.32907000 Z=0.20202000
      -2: X=0.67093000 Y=0.67093000 Z=0.20202000
Ru         NPT=  781  R0=.000010000 RMT=   2.45000   Z:  44.00000
LOCAL ROT MATRIX:    1.0000000 0.0000000 0.0000000
                     0.0000000 1.0000000 0.0000000
                     0.0000000 0.0000000 1.0000000
ATOM  -3: X=0.67093000 Y=0.00000000 Z=0.13571000
          MULT= 3          ISPLIT=15
      -3: X=0.00000000 Y=0.67093000 Z=0.13571000
      -3: X=0.32907000 Y=0.32907000 Z=0.13571000
Ru         NPT=  781  R0=.000010000 RMT=   2.45000   Z:  44.00000
LOCAL ROT MATRIX:    1.0000000 0.0000000 0.0000000
                     0.0000000 1.0000000 0.0000000
                     0.0000000 0.0000000 1.0000000
ATOM  -4: X=0.33333333 Y=0.00000000 Z=0.06761000
          MULT= 3          ISPLIT=15
      -4: X=0.00000000 Y=0.33333333 Z=0.06761000
      -4: X=0.66666667 Y=0.66666667 Z=0.06761000
Ru         NPT=  781  R0=.000010000 RMT=   2.45000   Z:  44.00000
LOCAL ROT MATRIX:    1.0000000 0.0000000 0.0000000
                     0.0000000 1.0000000 0.0000000
                     0.0000000 0.0000000 1.0000000
ATOM  -5: X=0.33333333 Y=0.33333333 Z=0.00000000
          MULT= 3          ISPLIT=15
      -5: X=0.66666667 Y=0.00000000 Z=0.00000000
      -5: X=0.00000000 Y=0.66666667 Z=0.00000000
Ru         NPT=  781  R0=.000010000 RMT=   2.45000   Z:  44.00000
LOCAL ROT MATRIX:    1.0000000 0.0000000 0.0000000
                     0.0000000 1.0000000 0.0000000
                     0.0000000 0.0000000 1.0000000
ATOM  -6: X=0.33333333 Y=0.00000000 Z=0.93239000
          MULT= 3          ISPLIT=15
      -6: X=0.00000000 Y=0.33333333 Z=0.93239000
      -6: X=0.66666667 Y=0.66666667 Z=0.93239000
Ru         NPT=  781  R0=.000010000 RMT=   2.45000   Z:  44.00000
LOCAL ROT MATRIX:    1.0000000 0.0000000 0.0000000
                     0.0000000 1.0000000 0.0000000
                     0.0000000 0.0000000 1.0000000
ATOM  -7: X=0.67093000 Y=0.00000000 Z=0.86429000
          MULT= 3          ISPLIT=15
      -7: X=0.00000000 Y=0.67093000 Z=0.86429000
      -7: X=0.32907000 Y=0.32907000 Z=0.86429000
Ru         NPT=  781  R0=.000010000 RMT=   2.45000   Z:  44.00000
LOCAL ROT MATRIX:    1.0000000 0.0000000 0.0000000
                     0.0000000 1.0000000 0.0000000
                     0.0000000 0.0000000 1.0000000
ATOM  -8: X=0.32907000 Y=0.00000000 Z=0.79799000
          MULT= 3          ISPLIT=15
      -8: X=0.00000000 Y=0.32907000 Z=0.79799000
      -8: X=0.67093000 Y=0.67093000 Z=0.79799000
Ru         NPT=  781  R0=.000010000 RMT=   2.45000   Z:  44.00000
LOCAL ROT MATRIX:    1.0000000 0.0000000 0.0000000
                     0.0000000 1.0000000 0.0000000
                     0.0000000 0.0000000 1.0000000
ATOM  -9: X=0.00000000 Y=0.00000000 Z=0.73688000
          MULT= 1          ISPLIT=15
Cl         NPT=  781  R0=.000100000 RMT=   2.15000   Z:  17.00000
LOCAL ROT MATRIX:    1.0000000 0.0000000 0.0000000
                     0.0000000 1.0000000 0.0000000
                     0.0000000 0.0000000 1.0000000
   0      NUMBER OF SYMMETRY OPERATIONS