forked from lijiext/lammps
137 lines
4.7 KiB
Plaintext
137 lines
4.7 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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pair_style dpd/fdt command :h3
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pair_style dpd/fdt/energy command :h3
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[Syntax:]
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pair_style style args :pre
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style = {dpd/fdt} or {dpd/fdt/energy}
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args = list of arguments for a particular style :ul
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{dpd/fdt} args = T cutoff seed
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T = temperature (temperature units)
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cutoff = global cutoff for DPD interactions (distance units)
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seed = random # seed (positive integer)
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{dpd/fdt/energy} args = cutoff seed
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cutoff = global cutoff for DPD interactions (distance units)
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seed = random # seed (positive integer) :pre
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[Examples:]
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pair_style dpd/fdt 300.0 2.5 34387
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pair_coeff * * 3.0 1.0 2.5 :pre
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pair_style dpd/fdt/energy 2.5 34387
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pair_coeff * * 3.0 1.0 0.1 2.5 :pre
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[Description:]
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Styles {dpd/fdt} and {dpd/fdt/energy} set the fluctuation-dissipation
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theorem parameters and compute the conservative force for dissipative
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particle dynamics (DPD). The conservative force on atom I due to atom
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J is given by
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:c,image(Eqs/pair_dpd_conservative.jpg)
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where the weighting factor, omega_ij, varies between 0 and 1, and is
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chosen to have the following functional form:
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:c,image(Eqs/pair_dpd_omega.jpg)
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where Rij is a unit vector in the direction Ri - Rj, and Rc is the
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cutoff. Note that alternative definitions of the weighting function
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exist, but would have to be implemented as a separate pair style
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command.
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These pair style differ from the other dpd styles in that the
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dissipative and random forces are not computed within the pair style.
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This style can be combined with the "fix shardlow"_fix_shardlow.html
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to perform the stochastic integration of the dissipative and random
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forces through the Shardlow splitting algorithm approach.
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The pairwise energy associated with styles {dpd/fdt} and
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{dpd/fdt/energy} is only due to the conservative force term Fc, and is
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shifted to be zero at the cutoff distance Rc. The pairwise virial is
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calculated using only the conservative term.
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For style {dpd/fdt}, the fluctuation-dissipation theorem defines gamma
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to be set equal to sigma*sigma/(2 T), where T is the set point
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temperature specified as a pair style parameter in the above examples.
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This style can be combined with "fix shardlow"_fix_shardlow.html to
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perform DPD simulations under isothermal and isobaric conditions (see
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"(Lisal)"_#Lisal). The following coefficients must be defined for
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each pair of atoms types via the "pair_coeff"_pair_coeff.html command
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as in the examples above, or in the data file or restart files read by
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the "read_data"_read_data.html or "read_restart"_read_restart.html
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commands:
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A (force units)
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sigma (force*time^(1/2) units)
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cutoff (distance units) :ul
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The last coefficient is optional. If not specified, the global DPD
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cutoff is used.
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For style {dpd/fdt/energy}, the fluctuation-dissipation theorem
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defines gamma to be set equal to sigma*sigma/(2 dpdTheta), where
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dpdTheta is the average internal temperature for the pair.
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Furthermore, the fluctuation-dissipation defines alpha*alpha to be set
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equal to 2*kB*kappa, where kappa is the mesoparticle thermal
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conductivity parameter. This style can be combined with "fix
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shardlow"_fix_shardlow.html to perform DPD simulations under
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isoenergetic and isoenthalpic conditions (see "(Lisal)"_#Lisal). The
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following coefficients must be defined for each pair of atoms types
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via the "pair_coeff"_pair_coeff.html command as in the examples above,
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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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A (force units)
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sigma (force*time^(1/2) units)
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kappa (1/time units)
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cutoff (distance units) :ul
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The last coefficient is optional. If not specified, the global DPD
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cutoff is used.
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For style {dpd/fdt/energy}, the particle internal temperature is
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related to the particle internal energy through a mesoparticle
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equation of state. Thus, an an additional "fix eos"_fix.html must be
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specified.
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:line
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[Restrictions:]
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Pair styles {dpd/fdt} and {dpd/fdt/energy} are only available if
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LAMMPS is built with the USER-DPD package.
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Pair styles {dpd/fdt} and {dpd/fdt/energy} require use of the
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"communicate vel yes"_communicate.html option so that velocites are
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stored by ghost atoms.
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Pair style {dpd/fdt/energy} requires "atom_style dpd"_atom_style.html
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to be used in order to properly account for the particle internal
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energies and temperatures.
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[Related commands:]
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"pair_coeff"_pair_coeff.html, "fix shardlow"_fix_shardlow.html
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[Default:] none
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:line
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:link(Lisal)
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[(Lisal)] M. Lisal, J.K. Brennan, J. Bonet Avalos, "Dissipative
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particle dynamics as isothermal, isobaric, isoenergetic, and
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isoenthalpic conditions using Shardlow-like splitting algorithms.",
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J. Chem. Phys., 135, 204105 (2011).
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