forked from lijiext/lammps
97 lines
3.3 KiB
Plaintext
97 lines
3.3 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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improper_style ring command :h3
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improper_style ring/omp command :h3
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[Syntax:]
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improper_style ring :pre
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[Examples:]
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improper_style ring
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improper_coeff 1 8000 70.5 :pre
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[Description:]
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The {ring} improper style uses the potential
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:c,image(Eqs/improper_ring.jpg)
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where K is a prefactor, theta is the angle formed by the atoms
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specified by (i,j,k,l) indices and theta0 its equilibrium value.
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If the 4 atoms in an improper quadruplet (listed in the data file read
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by the "read_data"_read_data.html command) are ordered i,j,k,l then
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theta_{ijl} is the angle between atoms i,j and l, theta_{ijk} is the
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angle between atoms i,j and k, theta_{kjl} is the angle between atoms
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j,k, and l.
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The "ring" improper style implements the improper potential introduced
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by Destree et al., in Equation (9) of "(Destree)"_#Destree. This
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potential does not affect small amplitude vibrations but is used in an
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ad-hoc way to prevent the onset of accidentially large amplitude
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fluctuations leading to the occurrence of a planar conformation of the
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three bonds i-j, j-k and j-l, an intermediate conformation toward the
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chiral inversion of a methine carbon. In the "Impropers" section of
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data file four atoms: i, j, k and l are specified with i,j and l lying
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on the backbone of the chain and k specifying the chirality of j.
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The following coefficients must be defined for each improper type via
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the "improper_coeff"_improper_coeff.html command as in the example
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above, or in the data file or restart files read by the
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"read_data"_read_data.html or "read_restart"_read_restart.html
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commands:
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K (energy/radian^2)
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theta0 (degrees) :ul
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theta0 is specified in degrees, but LAMMPS converts it to radians
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internally; hence the units of K are in energy/radian^2.
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:line
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Styles with a {cuda}, {gpu}, {intel}, {kk}, {omp}, or {opt} suffix are
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functionally the same as the corresponding style without the suffix.
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They have been optimized to run faster, depending on your available
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hardware, as discussed in "Section_accelerate"_Section_accelerate.html
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of the manual. The accelerated styles take the same arguments and
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should produce the same results, except for round-off and precision
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issues.
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These accelerated styles are part of the USER-CUDA, GPU, USER-INTEL,
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KOKKOS, USER-OMP and OPT packages, respectively. They are only
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enabled if LAMMPS was built with those packages. See the "Making
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LAMMPS"_Section_start.html#start_3 section for more info.
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You can specify the accelerated styles explicitly in your input script
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by including their suffix, or you can use the "-suffix command-line
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switch"_Section_start.html#start_7 when you invoke LAMMPS, or you can
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use the "suffix"_suffix.html command in your input script.
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See "Section_accelerate"_Section_accelerate.html of the manual for
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more instructions on how to use the accelerated styles effectively.
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:line
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[Restrictions:]
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This improper style can only be used if LAMMPS was built with the
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USER-MISC package. See the "Making LAMMPS"_Section_start.html#start_3
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section for more info on packages.
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[Related commands:]
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"improper_coeff"_improper_coeff.html
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:link(Destree)
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[(Destree)] M. Destree, F. Laupretre, A. Lyulin, and J.-P. Ryckaert,
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J Chem Phys, 112, 9632 (2000).
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