mirror of https://github.com/lammps/lammps.git
114 lines
3.7 KiB
HTML
114 lines
3.7 KiB
HTML
<HTML>
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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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<HR>
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<H3>pair_style zbl command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>pair_style zbl inner outer
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</PRE>
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<UL><LI>inner = distance where switching function begins
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<LI>outer = global cutoff for ZBL interaction
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>pair_style zbl 3.0 4.0
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pair_coeff * * 73.0
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pair_coeff 1 1 14.0
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Style <I>zbl</I> computes the Ziegler-Biersack-Littmark (ZBL) screened nuclear
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repulsion for describing high-energy collisions between atoms.
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<A HREF = "#Ziegler">(Ziegler)</A>. It includes an additional switching function
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that ramps the energy, force, and curvature smoothly to zero
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between an inner and outer cutoff. The potential
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energy due to a pair of atoms at a distance r_ij is given by:
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</P>
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<CENTER><IMG SRC = "Eqs/pair_zbl.jpg">
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</CENTER>
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<P>where e is the electron
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charge, epsilon_0 is the electrical permittivity of vacuum, and
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Z_i and Z_j are the nuclear charges of the two atoms in electron
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charge units.
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The switching
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function S(r) is identical to that used by
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<A HREF = "pair_gromacs.html">pair_style lj/gromacs</A>.
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Here, the inner and outer cutoff are the same
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for all pairs of atom types.
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</P>
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<P>The following coefficient must be defined for each pair of atom types
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via the <A HREF = "pair_coeff.html">pair_coeff</A> command as in the examples above,
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or in the LAMMPS data file.
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Z can not be specified for two different atoms types.
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Therefore the lists of atom types I and atom types J must match.
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</P>
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<UL><LI>Z (electron charge)
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</UL>
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<P>Although Z must be defined for all atom type pairs I,J, it is only
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stored for individual atom types, i.e. when I = J. Z is normally equal
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to the atomic number of the atom type.
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</P>
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<P>IMPORTANT NOTE: The numerical values of the exponential decay
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constants in the screening function depend
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on the unit of distance. In the above equation they are given for
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units of angstroms. LAMMPS will automatically convert these values to
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the distance unit of the specified LAMMPS <A HREF = "units.html">units</A> setting.
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The values of Z should always be given in units of electron charge.
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</P>
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<HR>
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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 ZBL interaction
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is defined by the values of Z for the two atom types, as in
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the equation above.
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</P>
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<P>The ZBL pair style does not support the
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<A HREF = "pair_modify.html">pair_modify</A> shift option, since the ZBL
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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>This 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>This pair style does not write information to <A HREF = "restart.html">binary
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restart files</A>, so pair_style and pair_coeff commands
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must be specified in an input script that reads a restart file.
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</P>
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<P>This 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 = "Ziegler"></A>
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<P><B>(Ziegler)</B> J.F. Ziegler, J. P. Biersack and U. Littmark, "The
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Stopping and Range of Ions in Matter," Volume 1, Pergamon, 1985.
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</P>
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</HTML>
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