forked from lijiext/lammps
139 lines
5.1 KiB
Plaintext
139 lines
5.1 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 lubricate command :h3
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[Syntax:]
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pair_style lubricate mu squeeze shear pump twist cutinner cutoff T_target seed :pre
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mu = dynamic viscosity (dynamic viscosity units)
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squeeze = 0/1 for squeeze force off/on
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shear = 0/1 for shear force off/on
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pump = 0/1 for pump force off/on
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twist = 0/1 for twist force off/on
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cutinner = (distance units)
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cutoff = outer cutoff for interactions (distance units)
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T_target = desired temperature (temperature units)
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seed = random number seed (positive integer) :ul
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[Examples:]
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pair_style lubricate 1.5 1 1 1 0 2.3 2.4 1.3 5878598
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pair_coeff 1 1 1.8 2.0
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pair_coeff * * :pre
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[Description:]
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Style {lubricate} computes pairwise interactions between mono-disperse
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spherical particles via this formula from "(Ball and Melrose)"_#Ball
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:c,image(Eqs/pair_lubricate.jpg)
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which represents the dissipation W between two nearby particles due to
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their relative velocities in the presence of a background solvent with
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viscosity mu. Note that this is dynamic viscosity which has units of
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mass/distance/time, not kinematic viscosity.
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Rc is the outer cutoff specified in the pair_style command, the
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translational velocities of the 2 particles are v1 and v2, the angular
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velocities are w1 and w2, and n is the unit vector in the direction
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from particle 1 to 2. The 4 terms represent four modes of pairwise
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interaction: squeezing, shearing, pumping, and twisting. The 4 flags
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in the pair_style command turn on or off each of these modes by
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including or excluding each term. The 4 coefficients on each term are
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functions of the separation distance of the particles and the
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viscosity. Details are given in "(Ball and Melrose)"_#Ball, including
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the forces and torques that result from taking derivatives of this
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equation with respect to velocity (see Appendix A).
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Unlike most pair potentials, the two specified cutoffs (cutinner and
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cutoff) refer to the surface-to-surface separation between two
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particles, not center-to-center distance. Currently, this pair style
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can only be used for mono-disperse extended spheres (same radii), so
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that separation is r_ij - 2*radius, where r_ij is the center-to-center
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distance between the particles. Within the inner cutoff {cutinner},
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the forces and torques are evaluated at a separation of cutinner. The
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outer {cutoff} is the separation distance beyond which the pair-wise
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forces are zero.
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A Langevin thermostatting term is also added to the pairwise force,
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similar to that provided by the "fix langevin"_fix_langevin.html or
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"pair_style dpd"_pair_dpd.html commands. The target temperature for
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the thermostat is the specified {T_target}. The {seed} is used for
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the random numbers generated for the thermostat.
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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, or by mixing as described below:
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cutinner (distance units)
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cutoff (distance units) :ul
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The two coefficients are optional. If neither is specified, the two
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cutoffs specified in the pair_style command are used. Otherwise both
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must be specified.
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:line
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[Mixing, shift, table, tail correction, restart, rRESPA info]:
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For atom type pairs I,J and I != J, the two cutoff distances for this
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pair style can be mixed. The default mix value is {geometric}. See
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the "pair_modify" command for details.
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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.
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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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This style is part of the "colloid" package. It is only enabled if
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LAMMPS was built with that package. See the "Making
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LAMMPS"_Section_start.html#2_3 section for more info.
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This pair style requires that atoms store torque and a quaternion to
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represent their orientation, as defined by the
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"atom_style"_atom_style.html. It also require they store a per-type
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"shape"_shape.html. The particles cannot store a per-particle
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diameter or per-particle mass.
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All the shape settings must be for finite-size spheres. They cannot
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be point particles, nor can they be aspherical. Additionally all the
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shape types must specify particles of the same size, i.e. a
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monodisperse system.
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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(Ball)
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[(Ball)] Ball and Melrose, Physica A, 247, 444-472 (1997).
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