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<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 buck/coul command 

</H3>

<P><B>Syntax:</B>

</P>

<PRE>pair_style buck/coul flag_buck flag_coul cutoff (cutoff2) 

</PRE>

<UL><LI>flag_buck = <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 Buckingnham (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 buck/coul cut off 2.5

pair_style buck/coul cut long 2.5 4.0

pair_style buck/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>buck/coul</I> style computes a Buckingham potential (exp/6 instead of

Lennard-Jones 12/6) and Coulombic potential, given by

</P>

<CENTER><IMG SRC = "Eqs/pair_buck.jpg">

</CENTER>

<CENTER><IMG SRC = "Eqs/pair_coulomb.jpg">

</CENTER>

<P>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.

</P>

<P>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 <I>flag_lj</I> and <I>flag_coul</I>

settings.  The "<A HREF = "#Ismail">Ismail</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 Buckingham

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

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

<I>flag_lj</I> is set to <I>cut</I>, the Buckingham interactions are simply

cutoff, as with <A HREF = "pair_buck.html">pair_style buck</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_buck</I> is also set to long, then only the

<I>ewald/n</I> Kspace style can perform the long-range calculations for

both the Buckingham 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:

</P>

<UL><LI>A (energy units)

<LI>rho (distance units)

<LI>C (energy-distance^6 units)

<LI>cutoff (distance units)

<LI>cutoff2 (distance units) 

</UL>

<P>The second coefficient, rho, must be greater than zero.

</P>

<P>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

<I>flag_buck</I> set to <I>long</I>, you cannot specify a Buckingham cutoff for

an atom type pair, since only one global Buckingham 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, and rRESPA info</B>:

</P>

<P>This pair styles does not support mixing.  Thus, coefficients for all

I,J pairs must be specified explicitly.

</P>

<P>This pair style supports the <A HREF = "pair_modify.html">pair_modify</A> shift

option for the energy of the exp() and 1/r^6 portion of the pair

interaction, assuming <I>flag_buck</I> is <I>cut</I>.

</P>

<P>This pair style does not support the <A HREF = "pair_modify.html">pair_modify</A>

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.

</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 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>

<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><B>Related commands:</B>

</P>

<P><A HREF = "pair_coeff.html">pair_coeff</A>

</P>

<P><B>Default:</B> none

</P>

<HR>



<A NAME = "Ismail"></A>



<P><B>(Ismail)</B> Ismail, Tsige, In 't Veld, Grest, Molecular Physics

(accepted) (2007).

</P>

</HTML>

doc/pair_buck_coul.txt

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"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 buck/coul command :h3



[Syntax:]



pair_style buck/coul flag_buck flag_coul cutoff (cutoff2) :pre



flag_buck = {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 Buckingnham (and Coulombic if only 1 cutoff) (distance units) :l

cutoff2 = global cutoff for Coulombic (optional) (distance units) :l,ule



[Examples:]



pair_style buck/coul cut off 2.5

pair_style buck/coul cut long 2.5 4.0

pair_style buck/coul long long 2.5 4.0

pair_coeff * * 1 1

pair_coeff 1 1 1 3 4 :pre



[Description:]



The {buck/coul} style computes a Buckingham potential (exp/6 instead of

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).

doc/pair_lj_coul.html

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<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>

doc/pair_lj_coul.txt

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