forked from lijiext/lammps
git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@1086 f3b2605a-c512-4ea7-a41b-209d697bcdaa
This commit is contained in:
parent
bb5e1cb67f
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@ -363,8 +363,8 @@ full description:
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<TR ALIGN="center"><TD ><A HREF = "pair_class2.html">lj/class2/coul/long</A></TD><TD ><A HREF = "pair_lj.html">lj/cut</A></TD><TD ><A HREF = "pair_lj.html">lj/cut/opt</A></TD><TD ><A HREF = "pair_lj.html">lj/cut/coul/cut</A></TD></TR>
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<TR ALIGN="center"><TD ><A HREF = "pair_class2.html">lj/class2/coul/long</A></TD><TD ><A HREF = "pair_lj.html">lj/cut</A></TD><TD ><A HREF = "pair_lj.html">lj/cut/opt</A></TD><TD ><A HREF = "pair_lj.html">lj/cut/coul/cut</A></TD></TR>
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<TR ALIGN="center"><TD ><A HREF = "pair_lj.html">lj/cut/coul/debye</A></TD><TD ><A HREF = "pair_lj.html">lj/cut/coul/long</A></TD><TD ><A HREF = "pair_lj.html">lj/cut/coul/long/tip4p</A></TD><TD ><A HREF = "pair_lj_expand.html">lj/expand</A></TD></TR>
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<TR ALIGN="center"><TD ><A HREF = "pair_lj.html">lj/cut/coul/debye</A></TD><TD ><A HREF = "pair_lj.html">lj/cut/coul/long</A></TD><TD ><A HREF = "pair_lj.html">lj/cut/coul/long/tip4p</A></TD><TD ><A HREF = "pair_lj_expand.html">lj/expand</A></TD></TR>
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<TR ALIGN="center"><TD ><A HREF = "pair_lj_smooth.html">lj/smooth</A></TD><TD ><A HREF = "pair_lubricate.html">lubricate</A></TD><TD ><A HREF = "pair_meam.html">meam</A></TD><TD ><A HREF = "pair_morse.html">morse</A></TD></TR>
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<TR ALIGN="center"><TD ><A HREF = "pair_lj_smooth.html">lj/smooth</A></TD><TD ><A HREF = "pair_lubricate.html">lubricate</A></TD><TD ><A HREF = "pair_meam.html">meam</A></TD><TD ><A HREF = "pair_morse.html">morse</A></TD></TR>
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<TR ALIGN="center"><TD ><A HREF = "pair_morse.html">morse/opt</A></TD><TD ><A HREF = "pair_soft.html">soft</A></TD><TD ><A HREF = "pair_sw.html">sw</A></TD><TD ><A HREF = "pair_table.html">table</A></TD></TR>
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<TR ALIGN="center"><TD ><A HREF = "pair_morse.html">morse/opt</A></TD><TD ><A HREF = "pair_resquared.html">resquared</A></TD><TD ><A HREF = "pair_soft.html">soft</A></TD><TD ><A HREF = "pair_sw.html">sw</A></TD></TR>
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<TR ALIGN="center"><TD ><A HREF = "pair_tersoff.html">tersoff</A></TD><TD ><A HREF = "pair_yukawa.html">yukawa</A>
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<TR ALIGN="center"><TD ><A HREF = "pair_table.html">table</A></TD><TD ><A HREF = "pair_tersoff.html">tersoff</A></TD><TD ><A HREF = "pair_yukawa.html">yukawa</A>
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</TD></TR></TABLE></DIV>
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</TD></TR></TABLE></DIV>
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<P>These are pair styles contributed by users, which can be used if
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<P>These are pair styles contributed by users, which can be used if
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@ -511,6 +511,7 @@ full description:
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"meam"_pair_meam.html,
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"meam"_pair_meam.html,
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"morse"_pair_morse.html,
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"morse"_pair_morse.html,
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"morse/opt"_pair_morse.html,
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"morse/opt"_pair_morse.html,
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"resquared"_pair_resquared.html,
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"soft"_pair_soft.html,
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"soft"_pair_soft.html,
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"sw"_pair_sw.html,
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"sw"_pair_sw.html,
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"table"_pair_table.html,
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"table"_pair_table.html,
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@ -126,6 +126,7 @@ the pair_style command, and coefficients specified by the associated
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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_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_morse.html">pair_style morse</A> - Morse potential
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<LI><A HREF = "pair_morse.html">pair_style morse</A> - optimized version of Morse potential
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<LI><A HREF = "pair_morse.html">pair_style morse</A> - optimized version of Morse potential
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<LI><A HREF = "pair_resquared.html">pair_style resquared</A> - Everaers RE-Squared ellipsoidal 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_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_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_table.html">pair_style table</A> - tabulated pair potential
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@ -122,6 +122,7 @@ the pair_style command, and coefficients specified by the associated
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"pair_style meam"_pair_meam.html - modified embedded atom method (MEAM)
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"pair_style meam"_pair_meam.html - modified embedded atom method (MEAM)
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"pair_style morse"_pair_morse.html - Morse potential
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"pair_style morse"_pair_morse.html - Morse potential
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"pair_style morse"_pair_morse.html - optimized version of Morse potential
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"pair_style morse"_pair_morse.html - optimized version of Morse potential
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"pair_style resquared"_pair_resquared.html - Everaers RE-Squared ellipsoidal potential
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"pair_style soft"_pair_soft.html - Soft (cosine) potential
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"pair_style soft"_pair_soft.html - Soft (cosine) potential
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"pair_style sw"_pair_sw.html - Stillinger-Weber 3-body potential
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"pair_style sw"_pair_sw.html - Stillinger-Weber 3-body potential
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"pair_style table"_pair_table.html - tabulated pair potential
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"pair_style table"_pair_table.html - tabulated pair potential
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@ -0,0 +1,201 @@
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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>
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</CENTER>
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<HR>
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<H3>pair_style resquared 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 resquared cutoff
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</PRE>
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<UL><LI>cutoff = global cutoff for interactions (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 resquared 10.0
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pair_coeff * * 1.0 1.0 1.7 3.4 3.4 1.0 1.0 1.0
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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>resquared</I> computes the RE-squared anisotropic interaction
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<A HREF = "#Everaers">(Everaers,Babadi)</A> between pairs of ellipsoidal and/or
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spherical Lennard-Jones particles. For ellipsoidal interactions,
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the potential considers the ellipsoid as being comprised of small
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spheres of size sigma. LJ particles are a single sphere of size
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sigma. The distinction is made to allow the pair style to make
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efficient calculations of ellipsoid/solvent interactions.
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</P>
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<P>Details for the equations used are given in the references below
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and <A HREF = "#redoc">this document</A>.
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</P>
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<P>Use of this pair style requires the NVE, NVT, or NPT fixes
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with the <I>asphere</I> extension (e.g. <A HREF = "fix_nve_asphere.html">fix
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nve/asphere</A>) in order to integrate particle
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rotation. Additionally, <A HREF = "atom_style.html">atom_style ellipsoid</A> should
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be used since it defines the rotational state of the ellipsoidal
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particles and the <A HREF = "shape.html">shape</A> command should be used to
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specify ellipsoid diameters.
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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>A12 = Energy Prefactor/Hamaker constant (energy units)
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<LI>sigma = atomic interaction diameter (distance units)
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<LI>epsilon_i_a = relative well depth of type I for side-to-side interactions
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<LI>epsilon_i_b = relative well depth of type I for face-to-face interactions
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<LI>epsilon_i_c = relative well depth of type I for end-to-end interactions
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<LI>epsilon_j_a = relative well depth of type J for side-to-side interactions
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<LI>epsilon_j_b = relative well depth of type J for face-to-face interactions
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<LI>epsilon_j_c = relative well depth of type J for end-to-end interactions
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<LI>cutoff (distance units)
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</UL>
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<P>The parameters used depend on the type of particles interacting -
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ellipsoid or LJ sphere. The type of particle is determined by
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the diameters specified with the <A HREF = "shape.html">shape</A>
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command. LJ spheres have diameters equal to zero and thus
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represent a single particle with size sigma. The epsilon_i_* or
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epsilon_j_* parameters are ignored for LJ sphere interactions.
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The interactions between two LJ sphere particles are computed
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using the standard Lennard-Jones formula.
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</P>
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<P>A12 specifies the energy prefactor which depends on
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the type of particles interacting. For ellipsoid-ellipsoid
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interactions, A12 is the Hamaker constant as described in
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<A HREF = "#Everaers">(Everaers)</A>. In LJ units:
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</P>
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<CENTER><IMG SRC = "Eqs/pair_resquared.jpg">
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</CENTER>
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<P>where rho gives the number density of the spherical particles
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composing the ellipsoids and epsilon_LJ determines the
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interaction strength of the spherical particles.
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</P>
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<P>For ellipsoid-LJ sphere interactions, A12 gives the energy
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prefactor (see <A HREF = "Eqs/pair_resquared_extra.pdf">here</A> for details:
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</P>
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<CENTER><IMG SRC = "Eqs/pair_resquared2.jpg">
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</CENTER>
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<P>For LJ sphere-LJ sphere interactions, A12 is the standard
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epsilon used in Lennard-Jones pair styles:
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</P>
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<CENTER><IMG SRC = "Eqs/pair_resquared3.jpg">
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</CENTER>
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<P>sigma specifies the diameter of the continuous distribution of
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constituent particles within each ellipsoid used to model
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the RE-squared potential. Therefore, the effective shape
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of an ellipsoid is given by the specified diameters
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(see the <A HREF = "shape.html">shape</A> command) plus sigma.
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</P>
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<P>For large uniform molecules it has been shown that the epsilon_*_*
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energy parameters are approximately representable in terms of
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local contact curvatures <A HREF = "#Everaers">(Everaers)</A>:
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</P>
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<CENTER><IMG SRC = "Eqs/pair_resquared4.jpg">
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</CENTER>
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<P>where a, b, and c give the particle diameters.
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</P>
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<P>The last coefficient is optional. If not specified, the global
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cutoff specified in the pair_style command is used.
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</P>
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<P>The epsilon_i and epsilon_j coefficients are actually defined for atom
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types, not for pairs of atom types. Thus, in a series of pair_coeff
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commands, they only need to be specified once for each atom type.
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</P>
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<P>Specifically, if any of epsilon_i_a, epsilon_i_b, epsilon_i_c are
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non-zero, the three values are assigned to atom type I. If all the
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epsilon_i values are zero, they are ignored. If any of epsilon_j_a,
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epsilon_j_b, epsilon_j_c are non-zero, the three values are assigned
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to atom type J. If all three epsilon_i values are zero, they are
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ignored. Thus the typical way to define the epsilon_i and epsilon_j
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coefficients is to list their values in "pair_coeff I J" commands when
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I = J, but set them to 0.0 when I != J. If you do list them when I !=
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J, you should insure they are consistent with their values in other
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pair_coeff commands.
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</P>
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<P>Note that if this potential is being used as a sub-style of
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<A HREF = "pair_hybrid.html">pair_style hybrid</A>, and there is no "pair_coeff I I"
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setting made for RE-squared for a particular type I (because I-I
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interactions are computed by another hybrid pair potential), then you
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still need to insure the epsilon a,b,c coefficients are assigned to
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that type in a "pair_coeff I J" command.
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</P>
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<HR>
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<P><B>Mixing, shift, table, tail correction, per-atom energy/stress,
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restart, rRESPA info</B>:
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</P>
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<P>Automatic mixing is supported only between LJ sphere
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pairs due to the different meanings of the energy prefactors used
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to calculate the interactions and the implicit dependance of
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the ellipsoid-LJ sphere interaction on the equation for the
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Hamaker constant presented here. Mixing of sigma and epsilon
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followed by calculation of the energy prefactors using the
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equations above is recommended.
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</P>
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<P>This pair styles supports the <A HREF = "pair_modify.html">pair_modify</A> shift
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option for the energy of the Lennard-Jones portion of the pair
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interaction, but only for sphere-sphere interactions. There is no
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shifting performed for ellipsoidal interactions due to the anisotropic
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dependence of the interaction.
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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 <A HREF = "pair_modify.html">pair_modify</A>
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tail option for adding long-range tail corrections to energy and
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pressure.
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</P>
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<P>This pair style does not calculate per-atom energy and stress, as used
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by the <A HREF = "compute_epair_atom.html">compute epair/atom</A>, <A HREF = "compute_stress_atom.html">compute
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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 writes its information to <A HREF = "restart.html">binary restart
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files</A>, so pair_style and pair_coeff commands do not need
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to 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> keyword of the
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<A HREF = "run_style.html">run_style respa</A> command. It does not support the
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<I>inner</I>, <I>middle</I>, <I>outer</I> keywords of the <A HREF = "run_style.html">run_style
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command</A>.
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</P>
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<HR>
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<P><B>Restrictions:</B>
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</P>
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<P>This style is part of the "asphere" package. It is only enabled if
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LAMMPS was built with that package. See the <A HREF = "Section_start.html#2_3">Making
|
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LAMMPS</A> section for more info.
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</P>
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<P>The distance-of-closest-approach approximation used by LAMMPS becomes
|
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less accurate when high-aspect ratio ellipsoids are used.
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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>, <A HREF = "fix_nve_asphere.html">fix nve/asphere</A>,
|
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<A HREF = "compute_temp_asphere.html">compute temp/asphere</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 = "Everaers"></A>
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<P><B>(Everaers)</B> Everaers and Ejtehadi, Phys Rev E, 67, 041710 (2003).
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</P>
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<A NAME = "Babadi"></A>
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<P><B>(Berardi)</B> Babadi, Ejtehadi, Everaers, J Comp Phys, 219, 770-779 (2006).
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</P>
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</HTML>
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@ -0,0 +1,194 @@
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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 resquared command :h3
|
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|
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|
[Syntax:]
|
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|
|
||||||
|
pair_style resquared cutoff :pre
|
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|
|
||||||
|
cutoff = global cutoff for interactions (distance units) :ul
|
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|
|
||||||
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[Examples:]
|
||||||
|
|
||||||
|
pair_style resquared 10.0
|
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|
pair_coeff * * 1.0 1.0 1.7 3.4 3.4 1.0 1.0 1.0 :pre
|
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|
|
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|
[Description:]
|
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|
|
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|
Style {resquared} computes the RE-squared anisotropic interaction
|
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|
"(Everaers,Babadi)"_#Everaers between pairs of ellipsoidal and/or
|
||||||
|
spherical Lennard-Jones particles. For ellipsoidal interactions,
|
||||||
|
the potential considers the ellipsoid as being comprised of small
|
||||||
|
spheres of size sigma. LJ particles are a single sphere of size
|
||||||
|
sigma. The distinction is made to allow the pair style to make
|
||||||
|
efficient calculations of ellipsoid/solvent interactions.
|
||||||
|
|
||||||
|
:link(redoc,Eqs/pair_resquared_extra.pdf)
|
||||||
|
|
||||||
|
Details for the equations used are given in the references below
|
||||||
|
and "this document"_#redoc.
|
||||||
|
|
||||||
|
Use of this pair style requires the NVE, NVT, or NPT fixes
|
||||||
|
with the {asphere} extension (e.g. "fix
|
||||||
|
nve/asphere"_fix_nve_asphere.html) in order to integrate particle
|
||||||
|
rotation. Additionally, "atom_style ellipsoid"_atom_style.html should
|
||||||
|
be used since it defines the rotational state of the ellipsoidal
|
||||||
|
particles and the "shape"_shape.html command should be used to
|
||||||
|
specify ellipsoid diameters.
|
||||||
|
|
||||||
|
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:
|
||||||
|
|
||||||
|
A12 = Energy Prefactor/Hamaker constant (energy units)
|
||||||
|
sigma = atomic interaction diameter (distance units)
|
||||||
|
epsilon_i_a = relative well depth of type I for side-to-side interactions
|
||||||
|
epsilon_i_b = relative well depth of type I for face-to-face interactions
|
||||||
|
epsilon_i_c = relative well depth of type I for end-to-end interactions
|
||||||
|
epsilon_j_a = relative well depth of type J for side-to-side interactions
|
||||||
|
epsilon_j_b = relative well depth of type J for face-to-face interactions
|
||||||
|
epsilon_j_c = relative well depth of type J for end-to-end interactions
|
||||||
|
cutoff (distance units) :ul
|
||||||
|
|
||||||
|
The parameters used depend on the type of particles interacting -
|
||||||
|
ellipsoid or LJ sphere. The type of particle is determined by
|
||||||
|
the diameters specified with the "shape"_shape.html
|
||||||
|
command. LJ spheres have diameters equal to zero and thus
|
||||||
|
represent a single particle with size sigma. The epsilon_i_* or
|
||||||
|
epsilon_j_* parameters are ignored for LJ sphere interactions.
|
||||||
|
The interactions between two LJ sphere particles are computed
|
||||||
|
using the standard Lennard-Jones formula.
|
||||||
|
|
||||||
|
A12 specifies the energy prefactor which depends on
|
||||||
|
the type of particles interacting. For ellipsoid-ellipsoid
|
||||||
|
interactions, A12 is the Hamaker constant as described in
|
||||||
|
"(Everaers)"_#Everaers. In LJ units:
|
||||||
|
|
||||||
|
:c,image(Eqs/pair_resquared.jpg)
|
||||||
|
|
||||||
|
where rho gives the number density of the spherical particles
|
||||||
|
composing the ellipsoids and epsilon_LJ determines the
|
||||||
|
interaction strength of the spherical particles.
|
||||||
|
|
||||||
|
For ellipsoid-LJ sphere interactions, A12 gives the energy
|
||||||
|
prefactor (see "here"_Eqs/pair_resquared_extra.pdf for details:
|
||||||
|
|
||||||
|
:c,image(Eqs/pair_resquared2.jpg)
|
||||||
|
|
||||||
|
For LJ sphere-LJ sphere interactions, A12 is the standard
|
||||||
|
epsilon used in Lennard-Jones pair styles:
|
||||||
|
|
||||||
|
:c,image(Eqs/pair_resquared3.jpg)
|
||||||
|
|
||||||
|
sigma specifies the diameter of the continuous distribution of
|
||||||
|
constituent particles within each ellipsoid used to model
|
||||||
|
the RE-squared potential. Therefore, the effective shape
|
||||||
|
of an ellipsoid is given by the specified diameters
|
||||||
|
(see the "shape"_shape.html command) plus sigma.
|
||||||
|
|
||||||
|
For large uniform molecules it has been shown that the epsilon_*_*
|
||||||
|
energy parameters are approximately representable in terms of
|
||||||
|
local contact curvatures "(Everaers)"_#Everaers:
|
||||||
|
|
||||||
|
:c,image(Eqs/pair_resquared4.jpg)
|
||||||
|
|
||||||
|
where a, b, and c give the particle diameters.
|
||||||
|
|
||||||
|
The last coefficient is optional. If not specified, the global
|
||||||
|
cutoff specified in the pair_style command is used.
|
||||||
|
|
||||||
|
The epsilon_i and epsilon_j coefficients are actually defined for atom
|
||||||
|
types, not for pairs of atom types. Thus, in a series of pair_coeff
|
||||||
|
commands, they only need to be specified once for each atom type.
|
||||||
|
|
||||||
|
Specifically, if any of epsilon_i_a, epsilon_i_b, epsilon_i_c are
|
||||||
|
non-zero, the three values are assigned to atom type I. If all the
|
||||||
|
epsilon_i values are zero, they are ignored. If any of epsilon_j_a,
|
||||||
|
epsilon_j_b, epsilon_j_c are non-zero, the three values are assigned
|
||||||
|
to atom type J. If all three epsilon_i values are zero, they are
|
||||||
|
ignored. Thus the typical way to define the epsilon_i and epsilon_j
|
||||||
|
coefficients is to list their values in "pair_coeff I J" commands when
|
||||||
|
I = J, but set them to 0.0 when I != J. If you do list them when I !=
|
||||||
|
J, you should insure they are consistent with their values in other
|
||||||
|
pair_coeff commands.
|
||||||
|
|
||||||
|
Note that if this potential is being used as a sub-style of
|
||||||
|
"pair_style hybrid"_pair_hybrid.html, and there is no "pair_coeff I I"
|
||||||
|
setting made for RE-squared for a particular type I (because I-I
|
||||||
|
interactions are computed by another hybrid pair potential), then you
|
||||||
|
still need to insure the epsilon a,b,c coefficients are assigned to
|
||||||
|
that type in a "pair_coeff I J" command.
|
||||||
|
|
||||||
|
:line
|
||||||
|
|
||||||
|
[Mixing, shift, table, tail correction, per-atom energy/stress,
|
||||||
|
restart, rRESPA info]:
|
||||||
|
|
||||||
|
Automatic mixing is supported only between LJ sphere
|
||||||
|
pairs due to the different meanings of the energy prefactors used
|
||||||
|
to calculate the interactions and the implicit dependance of
|
||||||
|
the ellipsoid-LJ sphere interaction on the equation for the
|
||||||
|
Hamaker constant presented here. Mixing of sigma and epsilon
|
||||||
|
followed by calculation of the energy prefactors using the
|
||||||
|
equations above is recommended.
|
||||||
|
|
||||||
|
This pair styles supports the "pair_modify"_pair_modify.html shift
|
||||||
|
option for the energy of the Lennard-Jones portion of the pair
|
||||||
|
interaction, but only for sphere-sphere interactions. There is no
|
||||||
|
shifting performed for ellipsoidal interactions due to the anisotropic
|
||||||
|
dependence of the interaction.
|
||||||
|
|
||||||
|
The "pair_modify"_pair_modify.html table option is not relevant
|
||||||
|
for this pair style.
|
||||||
|
|
||||||
|
This pair style does not support the "pair_modify"_pair_modify.html
|
||||||
|
tail option for adding long-range tail corrections to energy and
|
||||||
|
pressure.
|
||||||
|
|
||||||
|
This pair style does not 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 can only be used via the {pair} keyword of the
|
||||||
|
"run_style respa"_run_style.html command. It does not support the
|
||||||
|
{inner}, {middle}, {outer} keywords of the "run_style
|
||||||
|
command"_run_style.html.
|
||||||
|
|
||||||
|
:line
|
||||||
|
|
||||||
|
[Restrictions:]
|
||||||
|
|
||||||
|
This style is part of the "asphere" 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.
|
||||||
|
|
||||||
|
The distance-of-closest-approach approximation used by LAMMPS becomes
|
||||||
|
less accurate when high-aspect ratio ellipsoids are used.
|
||||||
|
|
||||||
|
[Related commands:]
|
||||||
|
|
||||||
|
"pair_coeff"_pair_coeff.html, "fix nve/asphere"_fix_nve_asphere.html,
|
||||||
|
"compute temp/asphere"_compute_temp_asphere.html
|
||||||
|
|
||||||
|
[Default:] none
|
||||||
|
|
||||||
|
:line
|
||||||
|
|
||||||
|
:link(Everaers)
|
||||||
|
[(Everaers)] Everaers and Ejtehadi, Phys Rev E, 67, 041710 (2003).
|
||||||
|
|
||||||
|
:link(Babadi)
|
||||||
|
[(Berardi)] Babadi, Ejtehadi, Everaers, J Comp Phys, 219, 770-779 (2006).
|
|
@ -131,6 +131,7 @@ the pair_style command, and coefficients specified by the associated
|
||||||
<LI><A HREF = "pair_meam.html">pair_style meam</A> - modified embedded atom method (MEAM)
|
<LI><A HREF = "pair_meam.html">pair_style meam</A> - modified embedded atom method (MEAM)
|
||||||
<LI><A HREF = "pair_morse.html">pair_style morse</A> - Morse potential
|
<LI><A HREF = "pair_morse.html">pair_style morse</A> - Morse potential
|
||||||
<LI><A HREF = "pair_morse.html">pair_style morse</A> - optimized version of Morse potential
|
<LI><A HREF = "pair_morse.html">pair_style morse</A> - optimized version of Morse potential
|
||||||
|
<LI><A HREF = "pair_resquared.html">pair_style resquared</A> - Everaers RE-Squared ellipsoidal potential
|
||||||
<LI><A HREF = "pair_soft.html">pair_style soft</A> - Soft (cosine) potential
|
<LI><A HREF = "pair_soft.html">pair_style soft</A> - Soft (cosine) potential
|
||||||
<LI><A HREF = "pair_sw.html">pair_style sw</A> - Stillinger-Weber 3-body potential
|
<LI><A HREF = "pair_sw.html">pair_style sw</A> - Stillinger-Weber 3-body potential
|
||||||
<LI><A HREF = "pair_table.html">pair_style table</A> - tabulated pair potential
|
<LI><A HREF = "pair_table.html">pair_style table</A> - tabulated pair potential
|
||||||
|
|
|
@ -127,6 +127,7 @@ the pair_style command, and coefficients specified by the associated
|
||||||
"pair_style meam"_pair_meam.html - modified embedded atom method (MEAM)
|
"pair_style meam"_pair_meam.html - modified embedded atom method (MEAM)
|
||||||
"pair_style morse"_pair_morse.html - Morse potential
|
"pair_style morse"_pair_morse.html - Morse potential
|
||||||
"pair_style morse"_pair_morse.html - optimized version of Morse potential
|
"pair_style morse"_pair_morse.html - optimized version of Morse potential
|
||||||
|
"pair_style resquared"_pair_resquared.html - Everaers RE-Squared ellipsoidal potential
|
||||||
"pair_style soft"_pair_soft.html - Soft (cosine) potential
|
"pair_style soft"_pair_soft.html - Soft (cosine) potential
|
||||||
"pair_style sw"_pair_sw.html - Stillinger-Weber 3-body potential
|
"pair_style sw"_pair_sw.html - Stillinger-Weber 3-body potential
|
||||||
"pair_style table"_pair_table.html - tabulated pair potential
|
"pair_style table"_pair_table.html - tabulated pair potential
|
||||||
|
|
|
@ -23,14 +23,14 @@ pair_coeff * * SiC.tersoff Si C Si
|
||||||
</PRE>
|
</PRE>
|
||||||
<P><B>Description:</B>
|
<P><B>Description:</B>
|
||||||
</P>
|
</P>
|
||||||
<P>The <I>tersoff</I> style computes a 3-body <A HREF = "#Tersoff">Tersoff</A> potential
|
<P>The <I>tersoff</I> style computes a 3-body <A HREF = "#Tersoff_1">Tersoff</A> potential
|
||||||
for the energy E of a system of atoms as
|
for the energy E of a system of atoms as
|
||||||
</P>
|
</P>
|
||||||
<CENTER><IMG SRC = "Eqs/pair_tersoff.jpg">
|
<CENTER><IMG SRC = "Eqs/pair_tersoff_1.jpg">
|
||||||
</CENTER>
|
</CENTER>
|
||||||
<P>where f_R is a two-body term and f_A includes three-body interactions.
|
<P>where f_R is a two-body term and f_A includes three-body interactions.
|
||||||
The summations in the formula are over all neighbors J and K of atom I
|
The summations in the formula are over all neighbors J and K of atom I
|
||||||
within a cutoff distance = R + D.
|
within a cutoff distance = R + D.
|
||||||
</P>
|
</P>
|
||||||
<P>Only a single pair_coeff command is used with the <I>tersoff</I> style
|
<P>Only a single pair_coeff command is used with the <I>tersoff</I> style
|
||||||
which specifies a Tersoff potential file with parameters for all
|
which specifies a Tersoff potential file with parameters for all
|
||||||
|
@ -66,6 +66,8 @@ above:
|
||||||
<UL><LI>element 1 (the center atom in a 3-body interaction)
|
<UL><LI>element 1 (the center atom in a 3-body interaction)
|
||||||
<LI>element 2 (the atom bonded to the center atom)
|
<LI>element 2 (the atom bonded to the center atom)
|
||||||
<LI>element 3 (the atom influencing the 1-2 bond in a bond-order sense)
|
<LI>element 3 (the atom influencing the 1-2 bond in a bond-order sense)
|
||||||
|
<LI>m
|
||||||
|
<LI>gamma
|
||||||
<LI>lambda3 (1/distance units)
|
<LI>lambda3 (1/distance units)
|
||||||
<LI>c
|
<LI>c
|
||||||
<LI>d
|
<LI>d
|
||||||
|
@ -80,7 +82,7 @@ above:
|
||||||
<LI>A (energy units)
|
<LI>A (energy units)
|
||||||
</UL>
|
</UL>
|
||||||
<P>The n, beta, lambda2, B, lambda1, and A parameters are only used for
|
<P>The n, beta, lambda2, B, lambda1, and A parameters are only used for
|
||||||
two-body interactions. The lambda3, c, d, and costheta0 parameters
|
two-body interactions. The m, gamma, lambda3, c, d, and costheta0 parameters
|
||||||
are only used for three-body interactions. The R and D parameters
|
are only used for three-body interactions. The R and D parameters
|
||||||
are used for both two-body and three-body interactions. The
|
are used for both two-body and three-body interactions. The
|
||||||
non-annotated parameters are unitless.
|
non-annotated parameters are unitless.
|
||||||
|
@ -113,6 +115,38 @@ The parameters used only for two-body interactions
|
||||||
in entries whose 2nd and 3rd element are different (e.g. SiCSi)
|
in entries whose 2nd and 3rd element are different (e.g. SiCSi)
|
||||||
are not used for anything and can be set to 0.0 if desired.
|
are not used for anything and can be set to 0.0 if desired.
|
||||||
</P>
|
</P>
|
||||||
|
<P>We chose the above form so as to enable users to define
|
||||||
|
all commonly used variants of the Tersoff potential.
|
||||||
|
In particular, our form reduces to the original
|
||||||
|
Tersoff form when m = 3 and gamma = 1, while it reduces to the form of <A HREF = "#Albe">Albe
|
||||||
|
et al.</A> when beta = 1 and m = 1. Tersoff used a slightly
|
||||||
|
different but equivalent form for alloys, which we will refer to
|
||||||
|
as <A HREF = "#Tersoff_2">Tersoff_2</A>.
|
||||||
|
</P>
|
||||||
|
<P>LAMMPS parameter values for Tersoff_2 can be obtained as follows.
|
||||||
|
The parameters for species i and j can be calculated
|
||||||
|
using the Tersoff_2 mixing rules:
|
||||||
|
</P>
|
||||||
|
<CENTER><IMG SRC = "Eqs/pair_tersoff_2.jpg">
|
||||||
|
</CENTER>
|
||||||
|
<P>Values not shown are determined by the first atom type. Finally, the
|
||||||
|
Tersoff_2 parameters R and S must be converted to the LAMMPS parameters
|
||||||
|
R and D (R is different in both forms), using the following relations:
|
||||||
|
R=(R'+S')/2 and D=(S'-R')/2, where the primes indicate the Tersoff_2 parameters.
|
||||||
|
</P>
|
||||||
|
<P>In the potentials directory, the file SiCGe.tersoff
|
||||||
|
provides the LAMMPS parameters for Tersoff's various versions of Si, as well
|
||||||
|
as his alloy paramters for Si, C, and Ge. This file can be
|
||||||
|
used for pure Si, (three different versions), pure C, pure Ge, binary SiC, and binary SiGe.
|
||||||
|
LAMMPS will generate an error
|
||||||
|
if this file is used with any combination involving C and Ge, since there are no entries for
|
||||||
|
the GeC interactions (Tersoff did not publish parameters for this cross-interaction.)
|
||||||
|
Tersoff files are also provided for the SiC alloy (SiC.tersoff) and the GaN (GaN.tersoff)
|
||||||
|
alloys.
|
||||||
|
</P>
|
||||||
|
<P>Many thanks to Rutuparna Narulkar, David Farrell, and Xiaowang Zhou for helping clarify
|
||||||
|
how Tersoff parameters for alloys have been defined in various papers.
|
||||||
|
</P>
|
||||||
<HR>
|
<HR>
|
||||||
|
|
||||||
<P><B>Mixing, shift, table, tail correction, per-atom energy/stress,
|
<P><B>Mixing, shift, table, tail correction, per-atom energy/stress,
|
||||||
|
@ -164,8 +198,14 @@ appropriate units if your simulation doesn't use "metal" units.
|
||||||
</P>
|
</P>
|
||||||
<HR>
|
<HR>
|
||||||
|
|
||||||
<A NAME = "Tersoff"></A>
|
<A NAME = "Tersoff_1"></A>
|
||||||
|
|
||||||
<P><B>(Tersoff)</B> Tersoff, Phys Rev B, 37, 6991 (1988).
|
<A NAME = "Albe"></A><B>(Tersoff_1)</B> J. Tersoff, Phys Rev B, 37, 6991 (1988).
|
||||||
|
|
||||||
|
|
||||||
|
<A NAME = "Tersoff_2"></A><B>(Albe)</B> J. Nord, K. Albe, P. Erhartand K. Nordlund, J. Phys.: Condens. Matter, 15, 5649(2003).
|
||||||
|
|
||||||
|
|
||||||
|
<P><B>(Tersoff_2)</B> J. Tersoff, Phys Rev B, 39, 5566 (1989)
|
||||||
</P>
|
</P>
|
||||||
</HTML>
|
</HTML>
|
||||||
|
|
Loading…
Reference in New Issue