2011-08-30 02:44:24 +08:00
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<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>
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<H3>pair_style lj/cubic command
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</H3>
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2011-10-07 01:32:51 +08:00
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<H3>pair_style lj/cubic/omp command
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</H3>
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2011-08-30 02:44:24 +08:00
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<P><B>Syntax:</B>
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</P>
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<PRE>pair_style lj/cubic
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</PRE>
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<P><B>Examples:</B>
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</P>
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<PRE>pair_style lj/cubic
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pair_coeff * * 1.0 0.8908987
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>The <I>lj/cubic</I> style computes a truncated LJ interaction potential whose
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2011-08-31 02:01:33 +08:00
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energy and force are continuous everywhere.
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Inside the inflection point the interaction is identical to the
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standard 12/6 <A HREF = "pair_lj.html">Lennard-Jones</A> potential.
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The LJ function outside the inflection point is replaced
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2011-08-31 03:45:56 +08:00
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with a cubic function of distance. The energy, force, and second
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derivative are continuous at the inflection point.
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The cubic coefficient A3 is chosen so
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that both energy and force go to zero at the cutoff distance.
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Outside the cutoff distance the energy and force are zero.
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</P>
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<CENTER><IMG SRC = "Eqs/pair_lj_cubic.jpg">
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</CENTER>
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<P>The location of the inflection point rs is defined
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2011-08-30 02:44:24 +08:00
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by the LJ diameter, rs/sigma = (26/7)^1/6. The cutoff distance
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2011-08-31 03:45:56 +08:00
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is defined by rc/rs = 67/48 or rc/sigma = 1.737....
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The analytic expression for the
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2011-08-31 02:01:33 +08:00
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the cubic coefficient
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2011-08-31 03:45:56 +08:00
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A3*rmin^3/epsilon = 27.93... is given in the paper by
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2011-08-31 02:01:33 +08:00
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Holian and Ravelo <A HREF = "#Holian">(Holian)</A>.
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2011-08-30 02:44:24 +08:00
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</P>
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2011-08-31 06:36:20 +08:00
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<P>This potential is commonly used to study the shock mechanics
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of FCC solids, as in Ravelo et al. <A HREF = "#Ravelo">(Ravelo)</A>.
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2011-08-30 02:44:24 +08:00
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</P>
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2011-08-31 02:01:33 +08:00
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<P>The following coefficients must be defined for each pair of atom
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2011-08-30 02:44:24 +08:00
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types via the <A HREF = "pair_coeff.html">pair_coeff</A> command as in the example
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above, or in the data file or restart files read by the
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<A HREF = "read_data.html">read_data</A> or <A HREF = "read_restart.html">read_restart</A>
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commands, or by mixing as described below:
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</P>
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<UL><LI>epsilon (energy units)
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<LI>sigma (distance units)
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</UL>
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<P>Note that sigma is defined in the LJ formula as the zero-crossing
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distance for the potential, not as the energy minimum, which
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2011-08-31 02:01:33 +08:00
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is located at rmin = 2^(1/6)*sigma. In the above example, sigma = 0.8908987,
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so rmin = 1.
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2011-08-30 02:44:24 +08:00
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</P>
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<HR>
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2011-12-14 04:35:35 +08:00
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<P>Styles with a <I>cuda</I>, <I>gpu</I>, <I>omp</I>, or <I>opt</I> suffix are functionally
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the same as the corresponding style without the suffix. They have
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been optimized to run faster, depending on your available hardware, as
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discussed in <A HREF = "Section_accelerate.html">Section_accelerate</A> of the
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manual. The accelerated styles take the same arguments and should
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produce the same results, except for round-off and precision issues.
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2011-10-07 01:32:51 +08:00
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</P>
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<P>These accelerated styles are part of the USER-CUDA, GPU, USER-OMP and OPT
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packages, respectively. They are only enabled if LAMMPS was built with
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those packages. See the <A HREF = "Section_start.html#start_3">Making LAMMPS</A>
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section for more info.
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</P>
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<P>You can specify the accelerated styles explicitly in your input script
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by including their suffix, or you can use the <A HREF = "Section_start.html#start_7">-suffix command-line
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2011-10-07 01:32:51 +08:00
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switch</A> when you invoke LAMMPS, or you can
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use the <A HREF = "suffix.html">suffix</A> command in your input script.
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</P>
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2011-12-14 04:35:35 +08:00
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<P>See <A HREF = "Section_accelerate.html">Section_accelerate</A> of the manual for
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more instructions on how to use the accelerated styles effectively.
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2011-10-07 01:32:51 +08:00
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</P>
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<HR>
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2011-08-30 02:44:24 +08:00
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<P><B>Mixing, shift, table, tail correction, restart, rRESPA info</B>:
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</P>
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<P>For atom type pairs I,J and I != J, the epsilon and sigma coefficients
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and cutoff distance for all of the lj/cut pair styles can be mixed.
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The default mix value is <I>geometric</I>. See the "pair_modify" command
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for details.
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</P>
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<P>The lj/cubic pair style does not support the
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<A HREF = "pair_modify.html">pair_modify</A> shift option,
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since pair interaction is already smoothed to 0.0 at the
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cutoff.
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</P>
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<P>The <A HREF = "pair_modify.html">pair_modify</A> table option is not relevant
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for this pair style.
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</P>
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<P>The lj/cubic pair style does not support the
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<A HREF = "pair_modify.html">pair_modify</A> tail option for adding long-range tail
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corrections to energy and pressure, since there are no corrections for
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a potential that goes to 0.0 at the cutoff.
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</P>
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<P>The lj/cubic pair style writes its information to <A HREF = "restart.html">binary
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restart files</A>, so pair_style and pair_coeff commands do
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not need to be specified in an input script that reads a restart file.
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</P>
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<P>The lj/cubic pair style can only be used via the <I>pair</I>
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keyword of the <A HREF = "run_style.html">run_style respa</A> command. It does not
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support the <I>inner</I>, <I>middle</I>, <I>outer</I> keywords.
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</P>
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<HR>
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<P><B>Restrictions:</B> none
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</P>
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<P><B>Related commands:</B>
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</P>
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<P><A HREF = "pair_coeff.html">pair_coeff</A>
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</P>
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<P><B>Default:</B> none
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</P>
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<HR>
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<A NAME = "Holian"></A>
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2011-08-31 06:36:20 +08:00
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<A NAME = "Ravelo"></A><B>(Holian)</B> Holian and Ravelo, Phys Rev B, 51, 11275 (1995).
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<P><B>(Ravelo)</B> Ravelo, Holian, Germann and Lomdahl, Phys Rev B, 70, 014103 (2004).
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2011-08-30 02:44:24 +08:00
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</P>
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</HTML>
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