forked from lijiext/lammps
84 lines
2.7 KiB
Plaintext
84 lines
2.7 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 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 (integer > 0 and < 900000000) :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 T gamma),
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where T is a parameter in the pair_style command.
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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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[Restrictions:] none
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This style is part of the "dpd" package. It is only enabled if LAMMPS
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was built with those package. See the "Making
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LAMMPS"_Section_start.html#2_2 section for more info.
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The {dpd} potential does not support the
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"pair_modify"_pair_modify.hmtl {mix} option. Coefficients for all i,j
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pairs must be specified explicitly.
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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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[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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