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< li > angle_style cosine/shift/exp command< / li >
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< div class = "section" id = "angle-style-cosine-shift-exp-command" >
< span id = "index-0" > < / span > < h1 > angle_style cosine/shift/exp command< a class = "headerlink" href = "#angle-style-cosine-shift-exp-command" title = "Permalink to this headline" > ¶< / a > < / h1 >
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< div class = "section" id = "angle-style-cosine-shift-exp-omp-command" >
< h1 > angle_style cosine/shift/exp/omp command< a class = "headerlink" href = "#angle-style-cosine-shift-exp-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 > angle_style cosine/shift/exp
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< h2 > Examples< a class = "headerlink" href = "#examples" title = "Permalink to this headline" > ¶< / a > < / h2 >
< div class = "highlight-python" > < div class = "highlight" > < pre > angle_style cosine/shift/exp
angle_coeff * 10.0 45.0 2.0
< / pre > < / div >
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< div class = "section" id = "description" >
< h2 > Description< a class = "headerlink" href = "#description" title = "Permalink to this headline" > ¶< / a > < / h2 >
< p > The < em > cosine/shift/exp< / em > angle style uses the potential< / p >
< img alt = "_images/angle_cosine_shift_exp.jpg" class = "align-center" src = "_images/angle_cosine_shift_exp.jpg" / >
< p > where Umin, theta, and a are defined for each angle type.< / p >
< p > The potential is bounded between [-Umin:0] and the minimum is
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located at the angle theta0. The a parameter can be both positive or
negative and is used to control the spring constant at the
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equilibrium.< / p >
< p > The spring constant is given by k = A exp(A) Umin / [2 (Exp(a)-1)].
For a > 3, k/Umin = a/2 to better than 5% relative error. For negative
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values of the a parameter, the spring constant is essentially zero,
and anharmonic terms takes over. The potential is furthermore well
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behaved in the limit a -> 0, where it has been implemented to linear
order in a for a < 0.001. In this limit the potential reduces to the
cosineshifted potential.< / p >
< p > The following coefficients must be defined for each angle type via the
< a class = "reference internal" href = "angle_coeff.html" > < em > angle_coeff< / em > < / a > command as in the example above, or in
the data file or restart files read by the < 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:< / p >
< ul class = "simple" >
< li > umin (energy)< / li >
< li > theta (angle)< / li >
< li > A (real number)< / li >
< / ul >
< 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 >
< / div >
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< div class = "section" id = "restrictions" >
< h2 > Restrictions< a class = "headerlink" href = "#restrictions" title = "Permalink to this headline" > ¶< / a > < / h2 >
< p > This angle style can only be used if LAMMPS was built with the
USER-MISC package. See the < a class = "reference internal" href = "Section_start.html#start-3" > < span > Making LAMMPS< / span > < / a >
section for more info on packages.< / p >
< / 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 = "angle_coeff.html" > < em > angle_coeff< / em > < / a > ,
< code class = "xref doc docutils literal" > < span class = "pre" > angle_cosineshift< / span > < / code > ,
< code class = "xref doc docutils literal" > < span class = "pre" > dihedral_cosineshift< / span > < / code > < / p >
< p > < strong > Default:< / strong > none< / p >
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