Finally, one can look at the orientation of the principal axes of the motion with respect to the bond vectors. For details see section Reorienting a Coordinate Trajectory . The function of this class of properties is to extract the first four moments of either the positional or velocity time distribution for all atoms. The moment-spec specifies which moment or minimum or maximum of the distribution for each atom to extract. X , Y , and Z specify the x, y, and z components of the positions.
R specifies different things for different moments.
For the first moment, it is the distance between the origin and average coordinates. For the second through fourth moments, it is the second through fourth power of the moments summed together and then raised to the reciprocal of the moment order. For example, R M4 is PAX , which may be specified only for the second through fourth moments, causes the principal axis values to be used. Note that when PAX is not specified, the cross moment terms are not accessible. The same rules apply for VX , VY , VZ , and VR except they apply to velocities.