forked from lijiext/lammps
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<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>
|
||||
</CENTER>
|
||||
|
||||
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||||
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||||
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||||
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||||
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||||
<HR>
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<H3>pair_style buck/coul 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 buck/coul flag_buck flag_coul cutoff (cutoff2)
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</PRE>
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<UL><LI>flag_buck = <I>long</I> or <I>cut</I>
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<PRE> <I>long</I> = use Kspace long-range summation for the dispersion term 1/r^6
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<I>cut</I> = use a cutoff
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</PRE>
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<LI>flag_coul = <I>long</I> or <I>off</I>
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<PRE> <I>long</I> = use Kspace long-range summation for the Coulombic term 1/r
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<I>off</I> = omit the Coulombic term
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</PRE>
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<LI>cutoff = global cutoff for Buckingnham (and Coulombic if only 1 cutoff) (distance units)
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<LI>cutoff2 = global cutoff for Coulombic (optional) (distance units)
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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 buck/coul cut off 2.5
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pair_style buck/coul cut long 2.5 4.0
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pair_style buck/coul long long 2.5 4.0
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pair_coeff * * 1 1
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pair_coeff 1 1 1 3 4
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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>buck/coul</I> style computes a Buckingham potential (exp/6 instead of
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Lennard-Jones 12/6) and Coulombic potential, given by
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</P>
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<CENTER><IMG SRC = "Eqs/pair_buck.jpg">
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</CENTER>
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<CENTER><IMG SRC = "Eqs/pair_coulomb.jpg">
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</CENTER>
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<P>Rc is the cutoff. If one cutoff is specified in the pair_style
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command, it is used for both the Buckingham and Coulombic terms. If
|
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two cutoffs are specified, they are used as cutoffs for the Buckingham
|
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and Coulombic terms respectively.
|
||||
</P>
|
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<P>The purpose of this pair style is to capture long-range interactions
|
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resulting from both attractive 1/r^6 Buckingham and Coulombic 1/r
|
||||
interactions. This is done by use of the <I>flag_lj</I> and <I>flag_coul</I>
|
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settings. The "<A HREF = "#Ismail">Ismail</A> paper has more details on when it is
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appropriate to include long-range 1/r^6 interactions, using this
|
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potential.
|
||||
</P>
|
||||
<P>If <I>flag_lj</I> is set to <I>long</I>, no cutoff is used on the Buckingham
|
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1/r^6 dispersion term. The long-range portion is calculated by using
|
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the <A HREF = "kspace_style.html">kspace_style ewald/n</A> command. The specified
|
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Buckingham cutoff then determines which portion of the Buckingham
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interactions are computed directly by the pair potential versus which
|
||||
part is computed in reciprocal space via the Kspace style. If
|
||||
<I>flag_lj</I> is set to <I>cut</I>, the Buckingham interactions are simply
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cutoff, as with <A HREF = "pair_buck.html">pair_style buck</A>.
|
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</P>
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<P>If <I>flag_coul</I> is set to <I>long</I>, no cutoff is used on the Coulombic
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interactions. The long-range portion is calculated by using any
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style, including <I>ewald/n</I> of the <A HREF = "kspace_style.html">kspace_style</A>
|
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command. Note that if <I>flag_buck</I> is also set to long, then only the
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<I>ewald/n</I> Kspace style can perform the long-range calculations for
|
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both the Buckingham and Coulombic interactions. If <I>flag_coul</I> is set
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to <I>off</I>, Coulombic interactions are not computed.
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</P>
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<P>The following coefficients must be defined for each pair of atoms
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types via the <A HREF = "pair_coeff.html">pair_coeff</A> 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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<A HREF = "read_data.html">read_data</A> or <A HREF = "read_restart.html">read_restart</A>
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commands:
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</P>
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<UL><LI>A (energy units)
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<LI>rho (distance units)
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<LI>C (energy-distance^6 units)
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<LI>cutoff (distance units)
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<LI>cutoff2 (distance units)
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</UL>
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<P>The second coefficient, rho, must be greater than zero.
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</P>
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<P>The latter 2 coefficients are optional. If not specified, the global
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Buckingham and Coulombic cutoffs specified in the pair_style command
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are used. If only one cutoff is specified, it is used as the cutoff
|
||||
for both Buckingham and Coulombic interactions for this type pair. If
|
||||
both coefficients are specified, they are used as the Buckingham and
|
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Coulombic cutoffs for this type pair. Note that if you are using
|
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<I>flag_buck</I> set to <I>long</I>, you cannot specify a Buckingham cutoff for
|
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an atom type pair, since only one global Buckingham cutoff is allowed.
|
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Similarly, if you are using <I>flag_coul</I> set to <I>long</I>, you cannot
|
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specify a Coulombic cutoff for an atom type pair, since only one
|
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global Coulombic cutoff is allowed.
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</P>
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<HR>
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||||
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<P><B>Mixing, shift, table, tail correction, per-atom energy/stress,
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restart, and rRESPA info</B>:
|
||||
</P>
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<P>This pair styles does not support mixing. Thus, coefficients for all
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I,J pairs must be specified explicitly.
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</P>
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<P>This pair style supports the <A HREF = "pair_modify.html">pair_modify</A> shift
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option for the energy of the exp() and 1/r^6 portion of the pair
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interaction, assuming <I>flag_buck</I> is <I>cut</I>.
|
||||
</P>
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<P>This pair style does not support the <A HREF = "pair_modify.html">pair_modify</A>
|
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shift option for the energy of the Buckingham portion of the pair
|
||||
interaction.
|
||||
</P>
|
||||
<P>This pair style does not support the <A HREF = "pair_modify.html">pair_modify</A>
|
||||
table option since a tabulation capability has not yet been added to
|
||||
this potential.
|
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</P>
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<P>This pair style can calculate per-atom energy and stress, as used by
|
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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>
|
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commands.
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</P>
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<P>This pair style write 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>
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<P>This pair style supports the use of the <I>inner</I>, <I>middle</I>, and <I>outer</I>
|
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keywords of the <A HREF = "run_style.html">run_style respa</A> command, meaning the
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pairwise forces can be partitioned by distance at different levels of
|
||||
the rRESPA hierarchy. See the <A HREF = "run_style.html">run_style</A> command for
|
||||
details.
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</P>
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<HR>
|
||||
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<P><B>Restrictions:</B>
|
||||
</P>
|
||||
<P>This style is part of the "user-ewaldn" 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>
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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 = "Ismail"></A>
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<P><B>(Ismail)</B> Ismail, Tsige, In 't Veld, Grest, Molecular Physics
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(accepted) (2007).
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</P>
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</HTML>
|
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|
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@ -0,0 +1,149 @@
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"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 buck/coul command :h3
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[Syntax:]
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pair_style buck/coul flag_buck flag_coul cutoff (cutoff2) :pre
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flag_buck = {long} or {cut} :ulb,l
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{long} = use Kspace long-range summation for the dispersion term 1/r^6
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{cut} = use a cutoff :pre
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flag_coul = {long} or {off} :l
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||||
{long} = use Kspace long-range summation for the Coulombic term 1/r
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{off} = omit the Coulombic term :pre
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cutoff = global cutoff for Buckingnham (and Coulombic if only 1 cutoff) (distance units) :l
|
||||
cutoff2 = global cutoff for Coulombic (optional) (distance units) :l,ule
|
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[Examples:]
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|
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pair_style buck/coul cut off 2.5
|
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pair_style buck/coul cut long 2.5 4.0
|
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pair_style buck/coul long long 2.5 4.0
|
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pair_coeff * * 1 1
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pair_coeff 1 1 1 3 4 :pre
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||||
|
||||
[Description:]
|
||||
|
||||
The {buck/coul} style computes a Buckingham potential (exp/6 instead of
|
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Lennard-Jones 12/6) and Coulombic potential, given by
|
||||
|
||||
:c,image(Eqs/pair_buck.jpg)
|
||||
|
||||
:c,image(Eqs/pair_coulomb.jpg)
|
||||
|
||||
Rc is the cutoff. If one cutoff is specified in the pair_style
|
||||
command, it is used for both the Buckingham and Coulombic terms. If
|
||||
two cutoffs are specified, they are used as cutoffs for the Buckingham
|
||||
and Coulombic terms respectively.
|
||||
|
||||
The purpose of this pair style is to capture long-range interactions
|
||||
resulting from both attractive 1/r^6 Buckingham and Coulombic 1/r
|
||||
interactions. This is done by use of the {flag_lj} and {flag_coul}
|
||||
settings. The ""Ismail"_#Ismail paper has more details on when it is
|
||||
appropriate to include long-range 1/r^6 interactions, using this
|
||||
potential.
|
||||
|
||||
If {flag_lj} is set to {long}, no cutoff is used on the Buckingham
|
||||
1/r^6 dispersion term. The long-range portion is calculated by using
|
||||
the "kspace_style ewald/n"_kspace_style.html command. The specified
|
||||
Buckingham cutoff then determines which portion of the Buckingham
|
||||
interactions are computed directly by the pair potential versus which
|
||||
part is computed in reciprocal space via the Kspace style. If
|
||||
{flag_lj} is set to {cut}, the Buckingham interactions are simply
|
||||
cutoff, as with "pair_style buck"_pair_buck.html.
|
||||
|
||||
If {flag_coul} is set to {long}, no cutoff is used on the Coulombic
|
||||
interactions. The long-range portion is calculated by using any
|
||||
style, including {ewald/n} of the "kspace_style"_kspace_style.html
|
||||
command. Note that if {flag_buck} is also set to long, then only the
|
||||
{ewald/n} Kspace style can perform the long-range calculations for
|
||||
both the Buckingham and Coulombic interactions. If {flag_coul} is set
|
||||
to {off}, Coulombic interactions are not computed.
|
||||
|
||||
The following coefficients must be defined for each pair of atoms
|
||||
types via the "pair_coeff"_pair_coeff.html command as in the examples
|
||||
above, or in the data file or restart files read by the
|
||||
"read_data"_read_data.html or "read_restart"_read_restart.html
|
||||
commands:
|
||||
|
||||
A (energy units)
|
||||
rho (distance units)
|
||||
C (energy-distance^6 units)
|
||||
cutoff (distance units)
|
||||
cutoff2 (distance units) :ul
|
||||
|
||||
The second coefficient, rho, must be greater than zero.
|
||||
|
||||
The latter 2 coefficients are optional. If not specified, the global
|
||||
Buckingham and Coulombic cutoffs specified in the pair_style command
|
||||
are used. If only one cutoff is specified, it is used as the cutoff
|
||||
for both Buckingham and Coulombic interactions for this type pair. If
|
||||
both coefficients are specified, they are used as the Buckingham and
|
||||
Coulombic cutoffs for this type pair. Note that if you are using
|
||||
{flag_buck} set to {long}, you cannot specify a Buckingham cutoff for
|
||||
an atom type pair, since only one global Buckingham cutoff is allowed.
|
||||
Similarly, if you are using {flag_coul} set to {long}, you cannot
|
||||
specify a Coulombic cutoff for an atom type pair, since only one
|
||||
global Coulombic cutoff is allowed.
|
||||
|
||||
:line
|
||||
|
||||
[Mixing, shift, table, tail correction, per-atom energy/stress,
|
||||
restart, and rRESPA info]:
|
||||
|
||||
This pair styles does not support mixing. Thus, coefficients for all
|
||||
I,J pairs must be specified explicitly.
|
||||
|
||||
This pair style supports the "pair_modify"_pair_modify.html shift
|
||||
option for the energy of the exp() and 1/r^6 portion of the pair
|
||||
interaction, assuming {flag_buck} is {cut}.
|
||||
|
||||
This pair style does not support the "pair_modify"_pair_modify.html
|
||||
shift option for the energy of the Buckingham portion of the pair
|
||||
interaction.
|
||||
|
||||
This pair style does not support the "pair_modify"_pair_modify.html
|
||||
table option since a tabulation capability has not yet been added to
|
||||
this potential.
|
||||
|
||||
This pair style can calculate per-atom energy and stress, as used by
|
||||
the "compute epair/atom"_compute_epair_atom.html, "compute
|
||||
stress/atom"_compute_stress_atom.html, and "dump custom"_dump.html
|
||||
commands.
|
||||
|
||||
This pair style write its information to "binary restart
|
||||
files"_restart.html, so pair_style and pair_coeff commands do not need
|
||||
to be specified in an input script that reads a restart file.
|
||||
|
||||
This pair style supports the use of the {inner}, {middle}, and {outer}
|
||||
keywords of the "run_style respa"_run_style.html command, meaning the
|
||||
pairwise forces can be partitioned by distance at different levels of
|
||||
the rRESPA hierarchy. See the "run_style"_run_style.html command for
|
||||
details.
|
||||
|
||||
:line
|
||||
|
||||
[Restrictions:]
|
||||
|
||||
This style is part of the "user-ewaldn" package. It is only enabled
|
||||
if LAMMPS was built with that package. See the "Making
|
||||
LAMMPS"_Section_start.html#2_3 section for more info.
|
||||
|
||||
[Related commands:]
|
||||
|
||||
"pair_coeff"_pair_coeff.html
|
||||
|
||||
[Default:] none
|
||||
|
||||
:line
|
||||
|
||||
:link(Ismail)
|
||||
[(Ismail)] Ismail, Tsige, In 't Veld, Grest, Molecular Physics
|
||||
(accepted) (2007).
|
||||
|
|
@ -0,0 +1,169 @@
|
|||
<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 lj/coul command
|
||||
</H3>
|
||||
<P><B>Syntax:</B>
|
||||
</P>
|
||||
<PRE>pair_style lj/coul flag_lj flag_coul cutoff (cutoff2)
|
||||
</PRE>
|
||||
<UL><LI>flag_lj = <I>long</I> or <I>cut</I>
|
||||
|
||||
<PRE> <I>long</I> = use Kspace long-range summation for the dispersion term 1/r^6
|
||||
<I>cut</I> = use a cutoff
|
||||
</PRE>
|
||||
<LI>flag_coul = <I>long</I> or <I>off</I>
|
||||
|
||||
<PRE> <I>long</I> = use Kspace long-range summation for the Coulombic term 1/r
|
||||
<I>off</I> = omit the Coulombic term
|
||||
</PRE>
|
||||
<LI>cutoff = global cutoff for LJ (and Coulombic if only 1 cutoff) (distance units)
|
||||
|
||||
<LI>cutoff2 = global cutoff for Coulombic (optional) (distance units)
|
||||
</UL>
|
||||
<P><B>Examples:</B>
|
||||
</P>
|
||||
<PRE>pair_style lj/coul cut off 2.5
|
||||
pair_style lj/coul cut long 2.5 4.0
|
||||
pair_style lj/coul long long 2.5 4.0
|
||||
pair_coeff * * 1 1
|
||||
pair_coeff 1 1 1 3 4
|
||||
</PRE>
|
||||
<P><B>Description:</B>
|
||||
</P>
|
||||
<P>The <I>lj/coul</I> style computes the standard 12/6 Lennard-Jones and
|
||||
Coulombic potentials, given by
|
||||
</P>
|
||||
<CENTER><IMG SRC = "Eqs/pair_lj.jpg">
|
||||
</CENTER>
|
||||
<CENTER><IMG SRC = "Eqs/pair_coulomb.jpg">
|
||||
</CENTER>
|
||||
<P>where C is an energy-conversion constant, Qi and Qj are the charges on
|
||||
the 2 atoms, epsilon is the dielectric constant which can be set by
|
||||
the <A HREF = "dielectric.html">dielectric</A> command, and Rc is the cutoff. If
|
||||
one cutoff is specified in the pair_style command, it is used for both
|
||||
the LJ and Coulombic terms. If two cutoffs are specified, they are
|
||||
used as cutoffs for the LJ and Coulombic terms respectively.
|
||||
</P>
|
||||
<P>The purpose of this pair style is to capture long-range interactions
|
||||
resulting from both attractive 1/r^6 Lennard-Jones and Coulombic 1/r
|
||||
interactions. This is done by use of the <I>flag_lj</I> and <I>flag_coul</I>
|
||||
settings. The <A HREF = "#Veld">In 't Veld</A> paper has more details on when it is
|
||||
appropriate to include long-range 1/r^6 interactions, using this
|
||||
potential.
|
||||
</P>
|
||||
<P>If <I>flag_lj</I> is set to <I>long</I>, no cutoff is used on the LJ 1/r^6
|
||||
dispersion term. The long-range portion is calculated by using the
|
||||
<A HREF = "kspace_style.html">kspace_style ewald/n</A> command. The specified LJ
|
||||
cutoff then determines which portion of the LJ interactions are
|
||||
computed directly by the pair potential versus which part is computed
|
||||
in reciprocal space via the Kspace style. If <I>flag_lj</I> is set to
|
||||
<I>cut</I>, the LJ interactions are simply cutoff, as with <A HREF = "pair_lj.html">pair_style
|
||||
lj/cut</A>.
|
||||
</P>
|
||||
<P>If <I>flag_coul</I> is set to <I>long</I>, no cutoff is used on the Coulombic
|
||||
interactions. The long-range portion is calculated by using any
|
||||
style, including <I>ewald/n</I> of the <A HREF = "kspace_style.html">kspace_style</A>
|
||||
command. Note that if <I>flag_lj</I> is also set to long, then only the
|
||||
<I>ewald/n</I> Kspace style can perform the long-range calculations for
|
||||
both the LJ and Coulombic interactions. If <I>flag_coul</I> is set to
|
||||
<I>off</I>, Coulombic interactions are not computed.
|
||||
</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>epsilon (energy units)
|
||||
<LI>sigma (distance units)
|
||||
<LI>cutoff1 (distance units)
|
||||
<LI>cutoff2 (distance units)
|
||||
</UL>
|
||||
<P>Note that sigma is defined in the LJ formula as the zero-crossing
|
||||
distance for the potential, not as the energy minimum at 2^(1/6)
|
||||
sigma.
|
||||
</P>
|
||||
<P>The latter 2 coefficients are optional. If not specified, the global
|
||||
LJ and Coulombic cutoffs specified in the pair_style command are used.
|
||||
If only one cutoff is specified, it is used as the cutoff for both LJ
|
||||
and Coulombic interactions for this type pair. If both coefficients
|
||||
are specified, they are used as the LJ and Coulombic cutoffs for this
|
||||
type pair. Note that if you are using <I>flag_lj</I> set to <I>long</I>, you
|
||||
cannot specify a LJ cutoff for an atom type pair, since only one
|
||||
global LJ cutoff is allowed. Similarly, if you are using <I>flag_coul</I>
|
||||
set to <I>long</I>, you cannot specify a Coulombic cutoff for an atom type
|
||||
pair, since only one global Coulombic cutoff is allowed.
|
||||
</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 epsilon and sigma coefficients
|
||||
and cutoff distance for all of the lj/cut pair styles can be mixed.
|
||||
The default mix value is <I>geometric</I>. See the "pair_modify" command
|
||||
for details.
|
||||
</P>
|
||||
<P>This pair style supports the <A HREF = "pair_modify.html">pair_modify</A> shift
|
||||
option for the energy of the Lennard-Jones portion of the pair
|
||||
interaction, assuming <I>flag_lj</I> is <I>cut</I>.
|
||||
</P>
|
||||
<P>This pair style supports the <A HREF = "pair_modify.html">pair_modify</A> table
|
||||
option since it can tabulate the short-range portion of the long-range
|
||||
Coulombic interaction.
|
||||
</P>
|
||||
<P>This pair styles supports the <A HREF = "pair_modify.html">pair_modify</A> tail
|
||||
option for adding a long-range tail correction to the Lennard-Jones
|
||||
portion of the energy and pressure of the pair interaction, assuming
|
||||
<I>flag_lj</I> is <I>cut</I>.
|
||||
</P>
|
||||
<P>This pair style can 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 supports the use of the <I>inner</I>, <I>middle</I>, and <I>outer</I>
|
||||
keywords of the <A HREF = "run_style.html">run_style respa</A> command, meaning the
|
||||
pairwise forces can be partitioned by distance at different levels of
|
||||
the rRESPA hierarchy. See the <A HREF = "run_style.html">run_style</A> command for
|
||||
details.
|
||||
</P>
|
||||
<HR>
|
||||
|
||||
<P><B>Restrictions:</B>
|
||||
</P>
|
||||
<P>This style is part of the "user-ewaldn" 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>
|
||||
<P>On some 64-bit machines, compiling with -O3 appears to break the
|
||||
Coulombic tabling option used by the <I>lj/coul</I> style. See the
|
||||
"Additional build tips" section of the Making LAMMPS documentation
|
||||
pages for workarounds on this issue.
|
||||
</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 = "Veld"></A>
|
||||
|
||||
<P><B>(In 't Veld)</B> In 't Veld, Ismail, Grest, J Chem Phys (accepted) (2007).
|
||||
</P>
|
||||
</HTML>
|
||||
|
|
@ -0,0 +1,158 @@
|
|||
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
|
||||
|
||||
:link(lws,http://lammps.sandia.gov)
|
||||
:link(ld,Manual.html)
|
||||
:link(lc,Section_commands.html#comm)
|
||||
|
||||
:line
|
||||
|
||||
pair_style lj/coul command :h3
|
||||
|
||||
[Syntax:]
|
||||
|
||||
pair_style lj/coul flag_lj flag_coul cutoff (cutoff2) :pre
|
||||
|
||||
flag_lj = {long} or {cut} :ulb,l
|
||||
{long} = use Kspace long-range summation for the dispersion term 1/r^6
|
||||
{cut} = use a cutoff :pre
|
||||
flag_coul = {long} or {off} :l
|
||||
{long} = use Kspace long-range summation for the Coulombic term 1/r
|
||||
{off} = omit the Coulombic term :pre
|
||||
cutoff = global cutoff for LJ (and Coulombic if only 1 cutoff) (distance units) :l
|
||||
cutoff2 = global cutoff for Coulombic (optional) (distance units) :l,ule
|
||||
|
||||
[Examples:]
|
||||
|
||||
pair_style lj/coul cut off 2.5
|
||||
pair_style lj/coul cut long 2.5 4.0
|
||||
pair_style lj/coul long long 2.5 4.0
|
||||
pair_coeff * * 1 1
|
||||
pair_coeff 1 1 1 3 4 :pre
|
||||
|
||||
[Description:]
|
||||
|
||||
The {lj/coul} style computes the standard 12/6 Lennard-Jones and
|
||||
Coulombic potentials, given by
|
||||
|
||||
:c,image(Eqs/pair_lj.jpg)
|
||||
|
||||
:c,image(Eqs/pair_coulomb.jpg)
|
||||
|
||||
where C is an energy-conversion constant, Qi and Qj are the charges on
|
||||
the 2 atoms, epsilon is the dielectric constant which can be set by
|
||||
the "dielectric"_dielectric.html command, and Rc is the cutoff. If
|
||||
one cutoff is specified in the pair_style command, it is used for both
|
||||
the LJ and Coulombic terms. If two cutoffs are specified, they are
|
||||
used as cutoffs for the LJ and Coulombic terms respectively.
|
||||
|
||||
The purpose of this pair style is to capture long-range interactions
|
||||
resulting from both attractive 1/r^6 Lennard-Jones and Coulombic 1/r
|
||||
interactions. This is done by use of the {flag_lj} and {flag_coul}
|
||||
settings. The "In 't Veld"_#Veld paper has more details on when it is
|
||||
appropriate to include long-range 1/r^6 interactions, using this
|
||||
potential.
|
||||
|
||||
If {flag_lj} is set to {long}, no cutoff is used on the LJ 1/r^6
|
||||
dispersion term. The long-range portion is calculated by using the
|
||||
"kspace_style ewald/n"_kspace_style.html command. The specified LJ
|
||||
cutoff then determines which portion of the LJ interactions are
|
||||
computed directly by the pair potential versus which part is computed
|
||||
in reciprocal space via the Kspace style. If {flag_lj} is set to
|
||||
{cut}, the LJ interactions are simply cutoff, as with "pair_style
|
||||
lj/cut"_pair_lj.html.
|
||||
|
||||
If {flag_coul} is set to {long}, no cutoff is used on the Coulombic
|
||||
interactions. The long-range portion is calculated by using any
|
||||
style, including {ewald/n} of the "kspace_style"_kspace_style.html
|
||||
command. Note that if {flag_lj} is also set to long, then only the
|
||||
{ewald/n} Kspace style can perform the long-range calculations for
|
||||
both the LJ and Coulombic interactions. If {flag_coul} is set to
|
||||
{off}, Coulombic interactions are not computed.
|
||||
|
||||
The following coefficients must be defined for each pair of atoms
|
||||
types via the "pair_coeff"_pair_coeff.html command as in the examples
|
||||
above, or in the data file or restart files read by the
|
||||
"read_data"_read_data.html or "read_restart"_read_restart.html
|
||||
commands, or by mixing as described below:
|
||||
|
||||
epsilon (energy units)
|
||||
sigma (distance units)
|
||||
cutoff1 (distance units)
|
||||
cutoff2 (distance units) :ul
|
||||
|
||||
Note that sigma is defined in the LJ formula as the zero-crossing
|
||||
distance for the potential, not as the energy minimum at 2^(1/6)
|
||||
sigma.
|
||||
|
||||
The latter 2 coefficients are optional. If not specified, the global
|
||||
LJ and Coulombic cutoffs specified in the pair_style command are used.
|
||||
If only one cutoff is specified, it is used as the cutoff for both LJ
|
||||
and Coulombic interactions for this type pair. If both coefficients
|
||||
are specified, they are used as the LJ and Coulombic cutoffs for this
|
||||
type pair. Note that if you are using {flag_lj} set to {long}, you
|
||||
cannot specify a LJ cutoff for an atom type pair, since only one
|
||||
global LJ cutoff is allowed. Similarly, if you are using {flag_coul}
|
||||
set to {long}, you cannot specify a Coulombic cutoff for an atom type
|
||||
pair, since only one global Coulombic cutoff is allowed.
|
||||
|
||||
:line
|
||||
|
||||
[Mixing, shift, table, tail correction, per-atom energy/stress,
|
||||
restart, rRESPA info]:
|
||||
|
||||
For atom type pairs I,J and I != J, the epsilon and sigma coefficients
|
||||
and cutoff distance for all of the lj/cut pair styles can be mixed.
|
||||
The default mix value is {geometric}. See the "pair_modify" command
|
||||
for details.
|
||||
|
||||
This pair style supports the "pair_modify"_pair_modify.html shift
|
||||
option for the energy of the Lennard-Jones portion of the pair
|
||||
interaction, assuming {flag_lj} is {cut}.
|
||||
|
||||
This pair style supports the "pair_modify"_pair_modify.html table
|
||||
option since it can tabulate the short-range portion of the long-range
|
||||
Coulombic interaction.
|
||||
|
||||
This pair styles supports the "pair_modify"_pair_modify.html tail
|
||||
option for adding a long-range tail correction to the Lennard-Jones
|
||||
portion of the energy and pressure of the pair interaction, assuming
|
||||
{flag_lj} is {cut}.
|
||||
|
||||
This pair style can calculate per-atom energy and stress, as used by
|
||||
the "compute epair/atom"_compute_epair_atom.html, "compute
|
||||
stress/atom"_compute_stress_atom.html, and "dump custom"_dump.html
|
||||
commands.
|
||||
|
||||
This pair style writes its information to "binary restart
|
||||
files"_restart.html, so pair_style and pair_coeff commands do not need
|
||||
to be specified in an input script that reads a restart file.
|
||||
|
||||
This pair style supports the use of the {inner}, {middle}, and {outer}
|
||||
keywords of the "run_style respa"_run_style.html command, meaning the
|
||||
pairwise forces can be partitioned by distance at different levels of
|
||||
the rRESPA hierarchy. See the "run_style"_run_style.html command for
|
||||
details.
|
||||
|
||||
:line
|
||||
|
||||
[Restrictions:]
|
||||
|
||||
This style is part of the "user-ewaldn" package. It is only enabled
|
||||
if LAMMPS was built with that package. See the "Making
|
||||
LAMMPS"_Section_start.html#2_3 section for more info.
|
||||
|
||||
On some 64-bit machines, compiling with -O3 appears to break the
|
||||
Coulombic tabling option used by the {lj/coul} style. See the
|
||||
"Additional build tips" section of the Making LAMMPS documentation
|
||||
pages for workarounds on this issue.
|
||||
|
||||
[Related commands:]
|
||||
|
||||
"pair_coeff"_pair_coeff.html
|
||||
|
||||
[Default:] none
|
||||
|
||||
:line
|
||||
|
||||
:link(Veld)
|
||||
[(In 't Veld)] In 't Veld, Ismail, Grest, J Chem Phys (accepted) (2007).
|
||||
Loading…
Reference in New Issue