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< title > pair_style lj/cubic command — LAMMPS 15 May 2015 version documentation< / title >
2011-08-30 02:44:24 +08:00
2015-07-30 22:53:28 +08:00
2011-08-30 02:44:24 +08:00
2015-07-30 22:53:28 +08:00
2011-08-30 02:44:24 +08:00
2015-07-30 22:53:28 +08:00
2011-08-30 02:44:24 +08:00
2015-07-30 22:53:28 +08:00
2011-08-30 02:44:24 +08:00
2015-07-30 22:53:28 +08:00
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< li > pair_style lj/cubic command< / li >
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< span id = "index-0" > < / span > < h1 > pair_style lj/cubic command< a class = "headerlink" href = "#pair-style-lj-cubic-command" title = "Permalink to this headline" > ¶< / a > < / h1 >
< / div >
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< div class = "section" id = "pair-style-lj-cubic-gpu-command" >
< h1 > pair_style lj/cubic/gpu command< a class = "headerlink" href = "#pair-style-lj-cubic-gpu-command" title = "Permalink to this headline" > ¶< / a > < / h1 >
< / div >
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< div class = "section" id = "pair-style-lj-cubic-omp-command" >
< h1 > pair_style lj/cubic/omp command< a class = "headerlink" href = "#pair-style-lj-cubic-omp-command" title = "Permalink to this headline" > ¶< / a > < / h1 >
< div class = "section" id = "syntax" >
< h2 > Syntax< a class = "headerlink" href = "#syntax" title = "Permalink to this headline" > ¶< / a > < / h2 >
< div class = "highlight-python" > < div class = "highlight" > < pre > pair_style lj/cubic
< / pre > < / div >
< / div >
< / div >
< div class = "section" id = "examples" >
< h2 > Examples< a class = "headerlink" href = "#examples" title = "Permalink to this headline" > ¶< / a > < / h2 >
< div class = "highlight-python" > < div class = "highlight" > < pre > pair_style lj/cubic
pair_coeff * * 1.0 0.8908987
< / pre > < / div >
< / div >
< / div >
< div class = "section" id = "description" >
< h2 > Description< a class = "headerlink" href = "#description" title = "Permalink to this headline" > ¶< / a > < / h2 >
< p > The < em > lj/cubic< / em > style computes a truncated LJ interaction potential whose
energy and force are continuous everywhere.
Inside the inflection point the interaction is identical to the
standard 12/6 < a class = "reference internal" href = "pair_lj.html" > < em > Lennard-Jones< / em > < / a > potential.
The LJ function outside the inflection point is replaced
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with a cubic function of distance. The energy, force, and second
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derivative are continuous at the inflection point.
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The cubic coefficient A3 is chosen so
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that both energy and force go to zero at the cutoff distance.
Outside the cutoff distance the energy and force are zero.< / p >
< img alt = "_images/pair_lj_cubic.jpg" class = "align-center" src = "_images/pair_lj_cubic.jpg" / >
< p > The location of the inflection point rs is defined
by the LJ diameter, rs/sigma = (26/7)^1/6. The cutoff distance
is defined by rc/rs = 67/48 or rc/sigma = 1.737....
The analytic expression for the
the cubic coefficient
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A3*rmin^3/epsilon = 27.93... is given in the paper by
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Holian and Ravelo < a class = "reference internal" href = "#holian" > < span > (Holian)< / span > < / a > .< / p >
< p > This potential is commonly used to study the shock mechanics
of FCC solids, as in Ravelo et al. < a class = "reference internal" href = "#ravelo" > < span > (Ravelo)< / span > < / a > .< / p >
< p > The following coefficients must be defined for each pair of atom
types via the < a class = "reference internal" href = "pair_coeff.html" > < em > pair_coeff< / em > < / a > command as in the example
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above, or in the data file or restart files read by the
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< a class = "reference internal" href = "read_data.html" > < em > read_data< / em > < / a > or < a class = "reference internal" href = "read_restart.html" > < em > read_restart< / em > < / a >
commands, or by mixing as described below:< / p >
< ul class = "simple" >
< li > epsilon (energy units)< / li >
< li > sigma (distance units)< / li >
< / ul >
< p > Note that sigma is defined in the LJ formula as the zero-crossing
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distance for the potential, not as the energy minimum, which
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is located at rmin = 2^(1/6)*sigma. In the above example, sigma = 0.8908987,
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so rmin = 1.< / p >
< hr class = "docutils" / >
< p > Styles with a < em > cuda< / em > , < em > gpu< / em > , < em > intel< / em > , < em > kk< / em > , < em > omp< / em > , or < em > opt< / em > suffix are
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functionally the same as the corresponding style without the suffix.
They have been optimized to run faster, depending on your available
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hardware, as discussed in < a class = "reference internal" href = "Section_accelerate.html" > < em > Section_accelerate< / em > < / a >
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of the manual. The accelerated styles take the same arguments and
should produce the same results, except for round-off and precision
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issues.< / p >
< p > These accelerated styles are part of the USER-CUDA, GPU, USER-INTEL,
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KOKKOS, USER-OMP and OPT packages, respectively. They are only
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enabled if LAMMPS was built with those packages. See the < a class = "reference internal" href = "Section_start.html#start-3" > < span > Making LAMMPS< / span > < / a > section for more info.< / p >
< p > You can specify the accelerated styles explicitly in your input script
by including their suffix, or you can use the < a class = "reference internal" href = "Section_start.html#start-7" > < span > -suffix command-line switch< / span > < / a > when you invoke LAMMPS, or you can
use the < a class = "reference internal" href = "suffix.html" > < em > suffix< / em > < / a > command in your input script.< / p >
< p > See < a class = "reference internal" href = "Section_accelerate.html" > < em > Section_accelerate< / em > < / a > of the manual for
more instructions on how to use the accelerated styles effectively.< / p >
< hr class = "docutils" / >
< p > < strong > Mixing, shift, table, tail correction, restart, rRESPA info< / strong > :< / p >
< p > For atom type pairs I,J and I != J, the epsilon and sigma coefficients
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and cutoff distance for all of the lj/cut pair styles can be mixed.
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The default mix value is < em > geometric< / em > . See the “ pair_modify” command
for details.< / p >
< p > The lj/cubic pair style does not support the
< a class = "reference internal" href = "pair_modify.html" > < em > pair_modify< / em > < / a > shift option,
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since pair interaction is already smoothed to 0.0 at the
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cutoff.< / p >
< p > The < a class = "reference internal" href = "pair_modify.html" > < em > pair_modify< / em > < / a > table option is not relevant
for this pair style.< / p >
< p > The lj/cubic pair style does not support the
< a class = "reference internal" href = "pair_modify.html" > < em > pair_modify< / em > < / a > tail option for adding long-range tail
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corrections to energy and pressure, since there are no corrections for
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a potential that goes to 0.0 at the cutoff.< / p >
< p > The lj/cubic pair style writes its information to < a class = "reference internal" href = "restart.html" > < em > binary restart files< / em > < / 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 > The lj/cubic pair style can only be used via the < em > pair< / em >
keyword of the < a class = "reference internal" href = "run_style.html" > < em > run_style respa< / em > < / a > command. It does not
support the < em > inner< / em > , < em > middle< / em > , < em > outer< / em > keywords.< / p >
< / div >
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< div class = "section" id = "restrictions" >
< h2 > Restrictions< a class = "headerlink" href = "#restrictions" title = "Permalink to this headline" > ¶< / a > < / h2 >
< blockquote >
< div > none< / div > < / blockquote >
< / div >
< div class = "section" id = "related-commands" >
< h2 > Related commands< a class = "headerlink" href = "#related-commands" title = "Permalink to this headline" > ¶< / a > < / h2 >
< p > < a class = "reference internal" href = "pair_coeff.html" > < em > pair_coeff< / em > < / a > < / p >
< p > < strong > Default:< / strong > none< / p >
< hr class = "docutils" / >
< p id = "ravelo" > < span id = "holian" > < / span > < strong > (Holian)< / strong > Holian and Ravelo, Phys Rev B, 51, 11275 (1995).< / p >
< p > < strong > (Ravelo)< / strong > Ravelo, Holian, Germann and Lomdahl, Phys Rev B, 70, 014103 (2004).< / p >
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