forked from lijiext/lammps
137 lines
6.8 KiB
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137 lines
6.8 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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<H3>pair_coeff 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_coeff I J args
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</PRE>
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<UL><LI>I,J = atom types (see asterik form below)
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<LI>args = coefficients for one or more pairs of atom types
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>pair_coeff 1 2 1.0 1.0 2.5
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pair_coeff 2 * 1.0 1.0
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pair_coeff 3* 1*2 1.0 1.0 2.5
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pair_coeff * * 1.0 1.0
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pair_coeff * * nialhjea 1 1 2
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pair_coeff * 3 morse.table ENTRY1
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pair_coeff 1 2 lj/cut 1.0 1.0 2.5 (for pair_style hybrid)
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Specify the pairwise force field coefficients for one or more pairs of
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atom types. The number and meaning of the coefficients depends on the
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pair style. Pair coefficients can also be set in the data file read
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by the <A HREF = "read_data.html">read_data</A> command or in a restart file.
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</P>
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<P>I and J can be specified in one of two ways. Explicit numeric values
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can be used for each, as in the 1st example above. I <= J is
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required. LAMMPS sets the coefficients for the symmetric J,I
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interaction to the same values.
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</P>
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<P>A wild-card asterik can be used in place of in conjunction with the
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I,J arguments to set the coefficients for multiple pairs of atom
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types. This takes the form "*" or "*n" or "n*" or "m*n". If N = the
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number of atom types, then an asterik with no numeric values means all
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types from 1 to N. A leading asterik means all types from 1 to n
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(inclusive). A trailing asterik means all types from n to N
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(inclusive). A middle asterik means all types from m to n
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(inclusive). Note that only type pairs with I <= J are considered; if
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asteriks imply type pairs where J < I, they are ignored.
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</P>
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<P>Note that a pair_coeff command can override a previous setting for the
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same I,J pair. For example, these commands set the coeffs for all I,J
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pairs, then overwrite the coeffs for just the I,J = 2,3 pair:
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</P>
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<PRE>pair_coeff * * 1.0 1.0 2.5
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pair_coeff 2 3 2.0 1.0 1.12
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</PRE>
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<P>A line in a data file that specifies pair coefficients uses the exact
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same format as the arguments of the pair_coeff command in an input
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script, with the exception of the I,J type arguments. In each line of
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the "Pair Coeffs" section of a data file, only a single type I is
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specified, which sets the coefficients for type I interacting with
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type I. This is because the section has exactly N lines, where N =
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the number of atom types. For this reason, the wild-card asterik
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should also not be used as part of the I argument. Thus in a data
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file, the line corresponding to the 1st example above would be listed
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as
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</P>
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<PRE>2 1.0 1.0 2.5
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</PRE>
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<P>If coefficients for type pairs with I not equal J are not set
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explicity by a pair_coeff command, they are inferred from the I,I and
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J,J settings by mixing rules; see the <A HREF = "pair_modify.html">pair_modify</A>
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command for a discussion. Exceptions to the mixing rules of the
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pair_modify command are discussed with the individual pair styles.
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</P>
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<HR>
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<P>Here is an alphabetic list of pair styles defined in LAMMPS. Click on
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the style to display the formula it computes, arguments specified in
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the pair_style command, and coefficients specified by the associated
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<A HREF = "pair_coeff.html">pair_coeff</A> command:
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</P>
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<UL><LI><A HREF = "pair_none.html">pair_style none</A> - turn off pairwise interactions
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<LI><A HREF = "pair_hybrid.html">pair_style hybrid</A> - define multiple styles of pairwise interactions
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</UL>
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<UL><LI><A HREF = "pair_buck.html">pair_style buck</A> - Buckingham potential
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<LI><A HREF = "pair_buck.html">pair_style buck/coul/cut</A> - Buckinhham with cutoff Coulomb
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<LI><A HREF = "pair_buck.html">pair_style buck/coul/long</A> - Buckingham with long-range Coulomb
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<LI><A HREF = "pair_dpd.html">pair_style dpd</A> - dissipative particle dynamics (DPD)
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<LI><A HREF = "pair_eam.html">pair_style eam</A> - embedded atom method (EAM)
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<LI><A HREF = "pair_eam.html">pair_style eam/alloy</A> - alloy EAM
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<LI><A HREF = "pair_eam.html">pair_style eam/fs</A> - Finnis-Sinclair EAM
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<LI><A HREF = "pair_granular.html">pair_style gran/hertzian</A> - granular potential with Hertizain interactions
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<LI><A HREF = "pair_granular.html">pair_style gran/history</A> - granular potential with history effects
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<LI><A HREF = "pair_granular.html">pair_style gran/no_history</A> - granular potential without history effects
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<LI><A HREF = "pair_charmm.html">pair_style lj/charmm/coul/charmm</A> - CHARMM potential with cutoff Coulomb
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<LI><A HREF = "pair_charmm.html">pair_style lj/charmm/coul/charmm/implicit</A> - CHARMM for implicit solvent
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<LI><A HREF = "pair_charmm.html">pair_style lj/charmm/coul/long</A> - CHARMM with long-range Coulomb
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<LI><A HREF = "pair_class2.html">pair_style lj/class2</A> - COMPASS (class 2) force field with no Coulomb
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<LI><A HREF = "pair_class2.html">pair_style lj/class2/coul/cut</A> - COMPASS with cutoff Coulomb
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<LI><A HREF = "pair_class2.html">pair_style lj/class2/coul/long</A> - COMPASS with long-range Coulomb
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<LI><A HREF = "pair_lj.html">pair_style lj/cut</A> - cutoff Lennard-Jones potential with no Coulomb
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<LI><A HREF = "pair_lj.html">pair_style lj/cut/coul/cut</A> - LJ with cutoff Coulomb
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<LI><A HREF = "pair_lj.html">pair_style lj/cut/coul/debye</A> - LJ with Debye damping added to Coulomb
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<LI><A HREF = "pair_lj.html">pair_style lj/cut/coul/long</A> - LJ with long-range Coulomb
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<LI><A HREF = "pair_lj.html">pair_style lj/cut/coul/long/tip4p</A> - LJ with long-range Coulomb for TIP4P water
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<LI><A HREF = "pair_lj_expand.html">pair_style lj/expand</A> - Lennard-Jones for variable size particles
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<LI><A HREF = "pair_lj_smooth.html">pair_style lj/smooth</A> - smoothed Lennard-Jones potential
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<LI><A HREF = "pair_meam.html">pair_style meam</A> - modified embedded atom method (MEAM)
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<LI><A HREF = "pair_morse.html">pair_style morse</A> - Morse potential
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<LI><A HREF = "pair_soft.html">pair_style soft</A> - Soft (cosine) potential
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<LI><A HREF = "pair_sw.html">pair_style sw</A> - Stillinger-Weber 3-body potential
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<LI><A HREF = "pair_table.html">pair_style table</A> - tabulated pair potential
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<LI><A HREF = "pair_tersoff.html">pair_style tersoff</A> - Tersoff 3-body potential
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<LI><A HREF = "pair_yukawa.html">pair_style yukawa</A> - Yukawa potential
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</UL>
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<HR>
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<P><B>Restrictions:</B>
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</P>
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<P>This command must come after the simulation box is defined by a
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<A HREF = "read_data.html">read_data</A>, <A HREF = "read_restart.html">read_restart</A>, or
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<A HREF = "create_box.html">create_box</A> command.
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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_style.html">pair_style</A>, <A HREF = "pair_modify.html">pair_modify</A>,
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<A HREF = "read_data.html">read_data</A>, <A HREF = "read_restart.html">read_restart</A>,
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<A HREF = "pair_write.html">pair_write</A>
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</P>
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<P><B>Default:</B> none
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</P>
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</HTML>
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