forked from lijiext/lammps
117 lines
3.9 KiB
Plaintext
117 lines
3.9 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 command :h3
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[Syntax:]
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pair_style dpd T cutoff seed :pre
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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) :ul
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[Examples:]
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pair_style dpd 1.0 2.5 34387
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pair_coeff * * 3.0 1.0
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pair_coeff 1 1 3.0 1.0 1.0 :pre
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[Description:]
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Style {dpd} computes a force field for dissipative particle dynamics
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(DPD) following the exposition in "(Groot)"_#Groot. The force
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on atom I due to atom J is given as a sum of 3 terms
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:c,image(Eqs/pair_dpd.jpg)
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where Fc is a conservative force, Fd is a dissipative force, and Fr is
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a random force. Rij is a unit vector in the direction Ri - Rj, Vij is
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the vector difference in velocities of the two atoms = Vi - Vj, alpha
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is a Gaussian random number with zero mean and unit variance, dt is
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the timestep size, and w(r) is a weighting factor that varies between
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0 and 1. Rc is the cutoff. Sigma is set equal to sqrt(2 Kb T gamma),
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where Kb is the Boltzmann constant and T is the temperature parameter
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in the pair_style command.
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The pairwise energy associated with this potential is only due to the
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conservative force term Fc.
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The following coefficients must be defined for each pair of atoms
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types via the "pair_coeff"_pair_coeff.html command as in the examples
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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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A (force units)
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gamma (force/velocity 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. Note that sigma is set equal to sqrt(2 T gamma),
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where T is the temperature set by the "pair_style"_pair_style.html
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command so it does not need to be specified.
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:line
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[Mixing, shift, table, tail correction, restart, rRESPA info]:
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This pair style does not support mixing. Thus, coefficients for all
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I,J pairs must be specified explicitly.
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This pair style does not support the "pair_modify"_pair_modify.html
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shift option for the energy of the pair interaction.
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The "pair_modify"_pair_modify.html table option is not relevant
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for this pair style.
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This pair style does not support the "pair_modify"_pair_modify.html
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tail option for adding long-range tail corrections to energy and
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pressure.
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This pair style writes its information to "binary restart
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files"_restart.html, so pair_style and pair_coeff commands do not need
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to be specified in an input script that reads a restart file. Note
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that the user-specified random number seed is stored in the restart
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file, so when a simulation is restarted, each processor will
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re-initialize its random number generator the same way it did
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initially. This means the random forces will be random, but will not
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be the same as they would have been if the original simulation had
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continued past the restart time.
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This pair style can only be used via the {pair} keyword of the
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"run_style respa"_run_style.html command. It does not support the
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{inner}, {middle}, {outer} keywords.
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:line
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[Restrictions:]
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The default frequency for rebuilding neighbor lists is every 10 steps
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(see the "neigh_modify"_neigh_modify.html command). This may be too
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infrequent for DPD simulations since particles move rapidly and can
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overlap by large amounts. If this setting yields a non-zero number of
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"dangerous" reneighborings (printed at the end of a simulation), you
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should experiment with forcing reneighboring more often and see if
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system energies/trajectories change.
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This pair style requires you to use the "communicate vel
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yes"_communicate.html option so that velocites are stored by ghost
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atoms.
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[Related commands:]
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"pair_coeff"_pair_coeff.html
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[Default:] none
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:line
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:link(Groot)
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[(Groot)] Groot and Warren, J Chem Phys, 107, 4423-35 (1997).
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