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Short helpfile for action PLANES
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The input trajectory can be in any of the following formats: 

                    MOL - The numerical indices of the atoms in the molecule. If 
                          three atoms are specified the orientation of the molecule is 
                          taken as the normal to the plane containing the vector connecting 
                          the first and second atoms and the vector connecting the second 
                          and third atoms. If four atoms are specified the orientation of 
                          the molecule is taken as the normal to the plane containing the 
                          vector connecting the first and second atoms and the vector 
                          connecting the third and fourth atoms. The molecule is always assumed 
                          to lie at the geometric center for the three/four atoms. You 
                          can use multiple instances of this keyword i.e. MOL1, MOL2, 
                          MOL3... 

The following options are available

  NUMERICAL_DERIVATIVES - ( default=off ) calculate the derivatives for these 
                          quantities numerically 
                  NOPBC - ( default=off ) ignore the periodic boundary conditions 
                          when calculating distances 
                 SERIAL - ( default=off ) do the calculation in serial. Do not use 
                          MPI 
                 LOWMEM - ( default=off ) lower the memory requirements 
                TIMINGS - ( default=off ) output information on the timings of the 
                          various parts of the calculation 
                  VMEAN - calculate the norm of the mean vector. The final value can 
                          be referenced using <em>label</em>.vmean. You can use multiple 
                          instances of this keyword i.e. VMEAN1, VMEAN2, VMEAN3... The 
                          corresponding values are then referenced using <em>label</em>.vmean-1, 
                          <em>label</em>.vmean-2, <em>label</em>.vmean-3... 


