forked from lijiext/lammps
71 lines
2.2 KiB
Plaintext
71 lines
2.2 KiB
Plaintext
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
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:link(lws,http://lammps.sandia.gov)
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:link(ld,Manual.html)
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:link(lc,Section_commands.html#comm)
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:line
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compute gyration command :h3
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[Syntax:]
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compute ID group-ID gyration :pre
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ID, group-ID are documented in "compute"_compute.html command
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gyration = style name of this compute command :ul
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[Examples:]
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compute 1 molecule gyration :pre
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[Description:]
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Define a computation that calculates the radius of gyration Rg of the
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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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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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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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See the "dump custom"_dump.html command for a discussion of
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"unwrapped" coordinates. See the Atoms section of the
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"read_data"_read_data.html command for a discussion of image flags and
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how they are set for each atom. You can reset the image flags
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(e.g. to 0) before invoking this compute by using the "set
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image"_set.html command.
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[Output info:]
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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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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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options.
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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.
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[Restrictions:] none
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[Related commands:]
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"compute gyration/molecule"_compute_gyration_molecule.html
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[Default:] none
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