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group of atoms, including all effects due to atoms passing thru
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periodic boundaries.
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Rg is a measure of the size of the group of atoms, and is computed by
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Rg is a measure of the size of the group of atoms, and is computed as
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the square root of the Rg^2 value in this formula
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:c,image(Eqs/compute_gyration.jpg)
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where M is the total mass of the group, Rcm is the center-of-mass
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position of the group, and the sum is over all atoms in the group.
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A Rg tensor, stored as a 6-element vector, is also calculated by this
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compute. The formula for the components of the tensor is the same as
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the above formula, except that (Ri - Rcm)^2 is replaced by (Rix -
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Rcmx) * (Riy - Rcmy) for the xy component, etc. The 6 components of
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the vector are ordered xx, yy, zz, xy, xz, yz.
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A Rg^2 tensor, stored as a 6-element vector, is also calculated by
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this compute. The formula for the components of the tensor is the
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same as the above formula, except that (Ri - Rcm)^2 is replaced by
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(Rix - Rcmx) * (Riy - Rcmy) for the xy component, etc. The 6
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components of the vector are ordered xx, yy, zz, xy, xz, yz. Note
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that unlike the scalar Rg, each of the 6 values of the tensor is
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effectively a "squared" value, since the cross-terms may be negative
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and taking a sqrt() would be invalid.
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IMPORTANT NOTE: The coordinates of an atom contribute to Rg in
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"unwrapped" form, by using the image flags associated with each atom.
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This compute calculates a global scalar (Rg) and a global vector of
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length 6 (Rg tensor), which can be accessed by indices 1-6. These
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length 6 (Rg^2 tensor), which can be accessed by indices 1-6. These
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values can be used by any command that uses a global scalar value or
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vector values from a compute as input. See "Section_howto
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15"_Section_howto.html#howto_15 for an overview of LAMMPS output
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The scalar and vector values calculated by this compute are
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"intensive". The scalar and vector values will be in distance
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"units"_units.html, since they are the square root of values
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represented by the formula above.
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"intensive". The scalar and vector values will be in distance and
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distance^2 "units"_units.html respectively.
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[Restrictions:] none