2007-10-12 07:52:34 +08:00
|
|
|
<HTML>
|
|
|
|
|
<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
|
|
|
|
|
</CENTER>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<HR>
|
|
|
|
|
|
|
|
|
|
<H3>pair_style lubricate command
|
|
|
|
|
</H3>
|
|
|
|
|
<P><B>Syntax:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<PRE>pair_style lubricate mu squeeze shear pump twist cutinner cutoff
|
|
|
|
|
</PRE>
|
2007-10-15 22:44:50 +08:00
|
|
|
<UL><LI>mu = viscosity (mass/distance/time units)
|
2007-10-12 07:52:34 +08:00
|
|
|
<LI>squeeze = 0/1 for squeeze force off/on
|
|
|
|
|
<LI>shear = 0/1 for shear force off/on
|
|
|
|
|
<LI>pump = 0/1 for pump force off/on
|
|
|
|
|
<LI>twist = 0/1 for twist force off/on
|
|
|
|
|
<LI>cutinner = (distance units)
|
|
|
|
|
<LI>cutoff = outer cutoff for interactions (distance units)
|
|
|
|
|
</UL>
|
|
|
|
|
<P><B>Examples:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<PRE>pair_style lubricate 1.5 1 1 1 0 2.3 2.4
|
|
|
|
|
pair_coeff 1 1 1.8 2.0
|
|
|
|
|
pair_coeff * *
|
|
|
|
|
</PRE>
|
|
|
|
|
<P><B>Description:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<P>Style <I>lubricate</I> computes pairwise interactions between mono-disperse
|
2007-10-12 22:50:04 +08:00
|
|
|
spherical particles via this formula from <A HREF = "#Ball">(Ball and Melrose)</A>
|
2007-10-12 07:52:34 +08:00
|
|
|
</P>
|
2007-10-12 22:50:04 +08:00
|
|
|
<CENTER><IMG SRC = "Eqs/pair_lubricate.jpg">
|
|
|
|
|
</CENTER>
|
|
|
|
|
<P>which represents the dissipation W between two nearby particles due to
|
|
|
|
|
the background solvent. Rc is the outer cutoff specified in the
|
|
|
|
|
pair_style command, the translational velocities of the 2 particles
|
|
|
|
|
are v1 and v2, the angular velocities are w1 and w2, and n is the unit
|
|
|
|
|
vector in the direction from particle 1 to 2. The 4 terms represent
|
|
|
|
|
four modes of pairwise interaction: squeezing, shearing, pumping, and
|
|
|
|
|
twisting. The 4 flags in the pair_style command turn on or off each
|
|
|
|
|
of these modes by including or excluding each term. The 4
|
|
|
|
|
coefficients on each term are functions of the separation distance of
|
|
|
|
|
the particles. Details are given in <A HREF = "#Ball">(Ball and Melrose)</A>,
|
|
|
|
|
including the forces and torques that result from taking derivatives
|
|
|
|
|
of this equation (see Appendix A).
|
2007-10-12 07:52:34 +08:00
|
|
|
</P>
|
|
|
|
|
<P>Unlike most pair potentials, the two specified cutoffs (cutinner and
|
|
|
|
|
cutoff) refer to the surface-to-surface separation between two
|
|
|
|
|
particles, not center-to-center distance. Currently, this pair style
|
|
|
|
|
can only be used for mono-disperse spheres (same radii), so that
|
|
|
|
|
separation is r_ij - 2*radius, where r_ij is the center-to-center
|
|
|
|
|
distance between the particles. Within the inner cutoff <I>cutinner</I>,
|
|
|
|
|
the forces and torques are evaluated at a separation of cutinner. The
|
|
|
|
|
outer <I>cutoff</I> is the separation distance beyond which the pair-wise
|
|
|
|
|
forces are zero.
|
|
|
|
|
</P>
|
|
|
|
|
<P>The following coefficients must be defined for each pair of atoms
|
|
|
|
|
types via the <A HREF = "pair_coeff.html">pair_coeff</A> command as in the examples
|
|
|
|
|
above, or in the data file or restart files read by the
|
|
|
|
|
<A HREF = "read_data.html">read_data</A> or <A HREF = "read_restart.html">read_restart</A>
|
|
|
|
|
commands, or by mixing as described below:
|
|
|
|
|
</P>
|
|
|
|
|
<UL><LI>cutinner (distance units)
|
|
|
|
|
<LI>cutoff (distance units)
|
|
|
|
|
</UL>
|
|
|
|
|
<P>The two coefficients are optional. If neither is specified, the two
|
|
|
|
|
cutoffs specified in the pair_style command are used. Otherwise both
|
|
|
|
|
must be specified.
|
|
|
|
|
</P>
|
|
|
|
|
<HR>
|
|
|
|
|
|
|
|
|
|
<P><B>Mixing, shift, table, tail correction, per-atom energy/stress,
|
|
|
|
|
restart, rRESPA info</B>:
|
|
|
|
|
</P>
|
|
|
|
|
<P>For atom type pairs I,J and I != J, the two cutoff distances for this
|
|
|
|
|
pair style can be mixed. The default mix value is <I>geometric</I>. See
|
|
|
|
|
the "pair_modify" command for details.
|
|
|
|
|
</P>
|
|
|
|
|
<P>This pair style does not support the <A HREF = "pair_modify.html">pair_modify</A>
|
|
|
|
|
shift option for the energy of the pair interaction.
|
|
|
|
|
</P>
|
|
|
|
|
<P>The <A HREF = "pair_modify.html">pair_modify</A> table option is not relevant
|
|
|
|
|
for this pair style.
|
|
|
|
|
</P>
|
|
|
|
|
<P>This pair style does not support the <A HREF = "pair_modify.html">pair_modify</A>
|
|
|
|
|
tail option for adding long-range tail corrections to energy and
|
|
|
|
|
pressure.
|
|
|
|
|
</P>
|
|
|
|
|
<P>This pair style does not calculate per-atom energy and stress, as used
|
|
|
|
|
by the <A HREF = "compute_epair_atom.html">compute epair/atom</A>, <A HREF = "compute_stress_atom.html">compute
|
|
|
|
|
stress/atom</A>, and <A HREF = "dump.html">dump custom</A>
|
|
|
|
|
commands.
|
|
|
|
|
</P>
|
|
|
|
|
<P>This pair style writes its information to <A HREF = "restart.html">binary restart
|
|
|
|
|
files</A>, so pair_style and pair_coeff commands do not need
|
|
|
|
|
to be specified in an input script that reads a restart file.
|
|
|
|
|
</P>
|
|
|
|
|
<P>This pair style can only be used via the <I>pair</I> keyword of the
|
|
|
|
|
<A HREF = "run_style.html">run_style respa</A> command. It does not support the
|
|
|
|
|
<I>inner</I>, <I>middle</I>, <I>outer</I> keywords.
|
|
|
|
|
</P>
|
|
|
|
|
<HR>
|
|
|
|
|
|
|
|
|
|
<P><B>Restrictions:</B>
|
|
|
|
|
</P>
|
2007-10-12 07:57:07 +08:00
|
|
|
<P>This style is part of the "colloid" package. It is only enabled if
|
|
|
|
|
LAMMPS was built with that package. See the <A HREF = "Section_start.html#2_3">Making
|
|
|
|
|
LAMMPS</A> section for more info.
|
|
|
|
|
</P>
|
2007-10-12 07:52:34 +08:00
|
|
|
<P>Because this poential computes forces and torques on particles, the
|
|
|
|
|
atom style must support particles whose size is set via the
|
|
|
|
|
<A HREF = "shape.html">shape</A> command. This is <A HREF = "atom_style.html">atom_style</A>
|
|
|
|
|
ellipsoid and dipole. Since only spherical mono-disperse particles
|
|
|
|
|
are currently allowed for pair_style lubricate, this means the 3 shape
|
|
|
|
|
radii for all particle types must be the same.
|
|
|
|
|
</P>
|
|
|
|
|
<P><B>Related commands:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<P><A HREF = "pair_coeff.html">pair_coeff</A>
|
|
|
|
|
</P>
|
|
|
|
|
<P><B>Default:</B> none
|
|
|
|
|
</P>
|
|
|
|
|
<HR>
|
|
|
|
|
|
|
|
|
|
<A NAME = "Ball"></A>
|
|
|
|
|
|
|
|
|
|
<P><B>(Ball)</B> Ball and Melrose, Physica A, 247, 444-472 (1997).
|
|
|
|
|
</P>
|
|
|
|
|
</HTML>
|
