Page Menu
Home
c4science
Search
Configure Global Search
Log In
Files
F110369441
dihedral_cosine_shift_exp.html
No One
Temporary
Actions
Download File
Edit File
Delete File
View Transforms
Subscribe
Mute Notifications
Award Token
Subscribers
None
File Metadata
Details
File Info
Storage
Attached
Created
Sat, Apr 26, 00:37
Size
3 KB
Mime Type
text/html
Expires
Mon, Apr 28, 00:37 (1 d, 23 h)
Engine
blob
Format
Raw Data
Handle
25813235
Attached To
rLAMMPS lammps
dihedral_cosine_shift_exp.html
View Options
<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>dihedral_style cosine/shift/exp command
</H3>
<H3>dihedral_style cosine/shift/exp/omp command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>dihedral_style cosine/shift/exp
</PRE>
<P><B>Examples:</B>
</P>
<PRE>dihedral_style cosine/shift/exp
dihedral_coeff 1 10.0 45.0 2.0
</PRE>
<P><B>Description:</B>
</P>
<P>The <I>cosine/shift/exp</I> dihedral style uses the potential
</P>
<CENTER><IMG SRC = "Eqs/dihedral_cosine_shift_exp.jpg">
</CENTER>
<P>where Umin, theta, and a are defined for each dihedral type.
</P>
<P>The potential is bounded between [-Umin:0] and the minimum is located
at the angle theta0. The a parameter can be both positive or negative
and is used to control the spring constant at the 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
values of the a parameter, the spring constant is essentially zero,
and anharmonic terms takes over. The potential is furthermore well
behaved in the limit a->0, where it has been implemented to linear
order in a for a < 0.001.
</P>
<P>The following coefficients must be defined for each dihedral type via
the <A HREF = "dihedral_coeff.html">dihedral_coeff</A> command as in the example
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>umin (energy)
<LI>theta (angle)
<LI>A (real number)
</UL>
<HR>
<P>Styles with a <I>cuda</I>, <I>gpu</I>, <I>omp</I>, or <I>opt</I> suffix are functionally
the same as the corresponding style without the suffix. They have
been optimized to run faster, depending on your available hardware, as
discussed in <A HREF = "Section_accelerate.html">Section_accelerate</A> of the
manual. The accelerated styles take the same arguments and should
produce the same results, except for round-off and precision issues.
</P>
<P>These accelerated styles are part of the USER-CUDA, GPU, USER-OMP and OPT
packages, respectively. They are only enabled if LAMMPS was built with
those packages. See the <A HREF = "Section_start.html#start_3">Making LAMMPS</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 HREF = "Section_start.html#start_6">-suffix command-line
switch</A> when you invoke LAMMPS, or you can
use the <A HREF = "suffix.html">suffix</A> command in your input script.
</P>
<P>See <A HREF = "Section_accelerate.html">Section_accelerate</A> of the manual for
more instructions on how to use the accelerated styles effectively.
</P>
<HR>
<P><B>Restrictions:</B>
</P>
<P>This dihedral style can only be used if LAMMPS was built with the
USER-MISC package. See the <A HREF = "Section_start.html#start_3">Making LAMMPS</A>
section for more info on packages.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "dihedral_coeff.html">dihedral_coeff</A>,
<A HREF = "angle_cosineshiftexp.html">angle_cosineshiftexp</A>
</P>
<P><B>Default:</B> none
</P>
</HTML>
Event Timeline
Log In to Comment