git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@15030 f3b2605a-c512-4ea7-a41b-209d697bcdaa
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sjplimp
@ -931,7 +931,6 @@ package"_Section_start.html#start_3.
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"coul/cut/soft (o)"_pair_lj_soft.html,
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"coul/diel (o)"_pair_coul_diel.html,
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"coul/long/soft (o)"_pair_lj_soft.html,
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"dpd/conservative"_pair_dpd_conservative.html,
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"dpd/fdt"_pair_dpd_fdt.html,
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"dpd/fdt/energy"_pair_dpd_fdt.html,
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"eam/cd (o)"_pair_eam.html,
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@ -957,6 +956,7 @@ package"_Section_start.html#start_3.
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"mgpt"_pair_mgpt.html,
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"morse/smooth/linear"_pair_morse.html,
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"morse/soft"_pair_morse.html,
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"multi/lucy"_pair_multi_lucy.html,
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"quip"_pair_quip.html,
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"reax/c"_pair_reax_c.html,
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"smd/hertz"_pair_smd_hertz.html,
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188
doc/src/pair_multi_lucy.txt
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188
doc/src/pair_multi_lucy.txt
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@ -0,0 +1,188 @@
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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 multi/lucy command :h3
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[Syntax:]
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pair_style multi/lucy style N keyword ... :pre
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style = {lookup} or {linear} = method of interpolation
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N = use N values in {lookup}, {linear} tables :ul
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[Examples:]
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pair_style multi/lucy linear 1000
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pair_coeff * * multibody.table ENTRY1 7.0 :pre
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[Description:]
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Style {multi/lucy} computes a density-dependent force following from the many-body
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form described in "(Moore)"_#Moore and "(Warren)"_#Warren as
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:c,image(Eqs/pair_multi_lucy.jpg)
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which consists of a density-dependent function, A(rho), and a radial-dependent weight
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function, omegaDD(rij). The radial-dependent weight function, omegaDD(rij), is taken
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as the Lucy function:
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:c,image(Eqs/pair_multi_lucy2.jpg)
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The density-dependent energy for a given particle is given by:
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:c,image(Eqs/pair_multi_lucy_energy.jpg)
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See the supporting information of "(Brennan)"_#Brennan or the publication by "(Moore)"_#Moore
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for more details on the functional form.
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An interpolation table is used to evaluate the density-dependent energy (Integral(A(rho)drho) and force (A(rho)).
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Note that the pre-factor to the energy is computed after the interpolation, thus the Integral(A(rho)drho will
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have units of energy / length^4.
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The interpolation table is created as a pre-computation by fitting cubic splines to
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the file values and interpolating the density-dependent energy and force at each of {N} densities.
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During a simulation, the tables are used to interpolate the density-dependent energy and force as
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needed for each pair of particles separated by a distance {R}. The interpolation is done in
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one of 2 styles: {lookup} and {linear}.
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For the {lookup} style, the density is used to find the nearest table entry, which is the
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density-dependent energy and force.
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For the {linear} style, the density is used to find the 2 surrounding table values from
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which the density-dependent energy and force are computed by linear interpolation.
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The following coefficients must be defined for each pair of atoms
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types via the "pair_coeff"_pair_coeff.html command as in the examples
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above.
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filename
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keyword
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cutoff (distance units) :ul
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The filename specifies a file containing the tabulated density-dependent
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energy and force. The keyword specifies a section of the file.
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The cutoff is an optional coefficient. If not specified, the outer cutoff in the
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table itself (see below) will be used to build an interpolation table
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that extend to the largest tabulated distance. If specified, only
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file values up to the cutoff are used to create the interpolation
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table. The format of this file is described below.
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:line
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The format of a tabulated file is a series of one or more sections,
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defined as follows (without the parenthesized comments):
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# Density-dependent function (one or more comment or blank lines) :pre
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DD-FUNCTION (keyword is first text on line)
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N 500 R 1.0 10.0 (N, R, RSQ parameters)
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(blank)
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1 1.0 25.5 102.34 (index, density, energy/r^4, force)
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2 1.02 23.4 98.5
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...
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500 10.0 0.001 0.003 :pre
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A section begins with a non-blank line whose 1st character is not a
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"#"; blank lines or lines starting with "#" can be used as comments
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between sections. The first line begins with a keyword which
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identifies the section. The line can contain additional text, but the
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initial text must match the argument specified in the pair_coeff
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command. The next line lists (in any order) one or more parameters
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for the table. Each parameter is a keyword followed by one or more
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numeric values.
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The parameter "N" is required and its value is the number of table
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entries that follow. Note that this may be different than the {N}
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specified in the "pair_style multi/lucy"_pair_multi_lucy.html command. Let
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Ntable = {N} in the pair_style command, and Nfile = "N" in the
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tabulated file. What LAMMPS does is a preliminary interpolation by
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creating splines using the Nfile tabulated values as nodal points. It
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uses these to interpolate the density-dependent energy and force at Ntable different
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points. The resulting tables of length Ntable are then used as
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described above, when computing the density-dependent energy and force.
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This means that if you want the interpolation tables of
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length Ntable to match exactly what is in the tabulated file (with
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effectively no preliminary interpolation), you should set Ntable =
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Nfile, and use the "RSQ" parameter. This is because the
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internal table abscissa is always RSQ (separation distance squared),
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for efficient lookup.
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All other parameters are optional. If "R" or "RSQ" does
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not appear, then the distances in each line of the table are used
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as-is to perform spline interpolation. In this case, the table values
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can be spaced in {density} uniformly or however you wish to position table
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values in regions of large gradients.
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If used, the parameters "R" or "RSQ" are followed by 2 values {rlo}
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and {rhi}. If specified, the density associated with each density-dependent
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energy and force value is computed from these 2 values (at high accuracy), rather
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than using the (low-accuracy) value listed in each line of the table.
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The density values in the table file are ignored in this case.
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For "R", distances uniformly spaced between {rlo} and {rhi} are
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computed; for "RSQ", squared distances uniformly spaced between
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{rlo*rlo} and {rhi*rhi} are computed.
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NOTE: If you use "R" or "RSQ", the tabulated distance values in the
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file are effectively ignored, and replaced by new values as described
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in the previous paragraph. If the density value in the table is not
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very close to the new value (i.e. round-off difference), then you will
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be assigning density-dependent energy and force values to a different density,
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which is probably not what you want. LAMMPS will warn if this is occurring.
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Following a blank line, the next N lines list the tabulated values.
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On each line, the 1st value is the index from 1 to N, the 2nd value is
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r (in density units), the 3rd value is the density-dependent function value
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(in energy units / length^4), and the 4th is the force (in force units). The
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density values must increase from one line to the next.
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Note that one file can contain many sections, each with a tabulated
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potential. LAMMPS reads the file section by section until it finds
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one that matches the specified keyword.
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:line
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[Mixing, shift, table, tail correction, restart, rRESPA info]:
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This pair style does not support mixing. Thus, coefficients for all
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I,J pairs must be specified explicitly.
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The "pair_modify"_pair_modify.html shift, table, and tail options are
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not relevant for this pair style.
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This pair style writes the settings for the "pair_style multi/lucy" command
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to "binary restart files"_restart.html, so a pair_style command does
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not need to specified in an input script that reads a restart file.
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However, the coefficient information is not stored in the restart
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file, since it is tabulated in the potential files. Thus, pair_coeff
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commands do need to be specified in the restart input script.
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This pair style can only be used via the {pair} keyword of the
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"run_style respa"_run_style.html command. It does not support the
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{inner}, {middle}, {outer} keywords.
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:line
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[Restrictions:] none
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[Related commands:]
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"pair_coeff"_pair_coeff.html
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[Default:] none
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:line
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:link(Warren)
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[(Warren)] Warren, Phys Rev E, 68, 066702 (2003).
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:link(Brennan)
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[(Brennan)] Brennan, J Chem Phys Lett, 5, 2144-2149 (2014).
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:link(Moore)
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[(Moore)] Moore, J Chem Phys, 144, 104501 (2016).
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