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Short helpfile for action GRADIENT
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The following arguments are compulsory: 

                 ORIGIN - we will use the position of this atom as the origin in our 
                          calculation 
                  NBINS - number of bins to use in each direction for the calculation 
                          of the gradient 
                    DIR - ( default=xyz ) the directions in which we are calculating 
                          the graident. Should be x, y, z, xy, xz, yz or xyz 
                  SIGMA - the width of the function to be used for kernel density 
                          estimation 
                 KERNEL - ( default=gaussian-bin ) the type of kernel function to be 
                          used in the grids 
                  ATOMS - calculate the gradient of these atoms 

