2009-08-11 04:13:44 +08:00
|
|
|
<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>angle_style table command
|
|
|
|
|
</H3>
|
|
|
|
|
<P><B>Syntax:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<PRE>angle_style table style N
|
|
|
|
|
</PRE>
|
|
|
|
|
<UL><LI>style = <I>linear</I> or <I>spline</I> = method of interpolation
|
|
|
|
|
<LI>N = use N values in table
|
|
|
|
|
</UL>
|
|
|
|
|
<P><B>Examples:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<PRE>angle_style table linear 1000
|
|
|
|
|
angle_coeff 3 file.table ENTRY1
|
|
|
|
|
</PRE>
|
|
|
|
|
<P><B>Description:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<P>Style <I>table</I> creates interpolation tables of length <I>N</I> from angle
|
2010-11-18 00:26:24 +08:00
|
|
|
potential and derivative values listed in a file(s) as a function of
|
|
|
|
|
angle The files are read by the <A HREF = "angle_coeff.html">angle_coeff</A>
|
|
|
|
|
command.
|
2009-08-11 04:13:44 +08:00
|
|
|
</P>
|
|
|
|
|
<P>The interpolation tables are created by fitting cubic splines to the
|
2010-11-18 00:26:24 +08:00
|
|
|
file values and interpolating energy and derivative values at each of
|
|
|
|
|
<I>N</I> angles. During a simulation, these tables are used to interpolate
|
|
|
|
|
energy and force values on individual atoms as needed. The
|
|
|
|
|
interpolation is done in one of 2 styles: <I>linear</I> or <I>spline</I>.
|
2009-08-11 04:13:44 +08:00
|
|
|
</P>
|
|
|
|
|
<P>For the <I>linear</I> style, the angle is used to find 2 surrounding table
|
2010-11-18 00:26:24 +08:00
|
|
|
values from which an energy or its derivative is computed by linear
|
2009-08-11 04:13:44 +08:00
|
|
|
interpolation.
|
|
|
|
|
</P>
|
|
|
|
|
<P>For the <I>spline</I> style, a cubic spline coefficients are computed and
|
|
|
|
|
stored at each of the <I>N</I> values in the table. The angle is used to
|
|
|
|
|
find the appropriate set of coefficients which are used to evaluate a
|
2010-11-18 00:26:24 +08:00
|
|
|
cubic polynomial which computes the energy or derivative.
|
2009-08-11 04:13:44 +08:00
|
|
|
</P>
|
|
|
|
|
<P>The following coefficients must be defined for each angle type via the
|
|
|
|
|
<A HREF = "angle_coeff.html">angle_coeff</A> command as in the example above.
|
|
|
|
|
</P>
|
|
|
|
|
<UL><LI>filename
|
|
|
|
|
<LI>keyword
|
|
|
|
|
</UL>
|
2010-11-18 00:26:24 +08:00
|
|
|
<P>The filename specifies a file containing tabulated energy and
|
|
|
|
|
derivative values. The keyword specifies a section of the file. The
|
|
|
|
|
format of this file is described below.
|
2009-08-11 04:13:44 +08:00
|
|
|
</P>
|
|
|
|
|
<HR>
|
|
|
|
|
|
|
|
|
|
<P>The format of a tabulated file is as follows (without the
|
|
|
|
|
parenthesized comments):
|
|
|
|
|
</P>
|
|
|
|
|
<PRE># Angle potential for harmonic (one or more comment or blank lines)
|
|
|
|
|
</PRE>
|
|
|
|
|
<PRE>HAM (keyword is the first text on line)
|
|
|
|
|
N 181 FP 0 0 EQ 90.0 (N, FP, EQ parameters)
|
|
|
|
|
(blank line)
|
|
|
|
|
N 181 FP 0 0 (N, FP parameters)
|
2010-11-18 00:26:24 +08:00
|
|
|
1 0.0 200.5 2.5 (index, angle, energy, derivative)
|
2009-08-11 04:13:44 +08:00
|
|
|
2 1.0 198.0 2.5
|
|
|
|
|
...
|
|
|
|
|
181 180.0 0.0 0.0
|
|
|
|
|
</PRE>
|
|
|
|
|
<P>A section begins with a non-blank line whose 1st character is not a
|
|
|
|
|
"#"; blank lines or lines starting with "#" can be used as comments
|
|
|
|
|
between sections. The first line begins with a keyword which
|
|
|
|
|
identifies the section. The line can contain additional text, but the
|
|
|
|
|
initial text must match the argument specified in the
|
|
|
|
|
<A HREF = "angle_coeff.html">angle_coeff</A> command. The next line lists (in any
|
|
|
|
|
order) one or more parameters for the table. Each parameter is a
|
|
|
|
|
keyword followed by one or more numeric values.
|
|
|
|
|
</P>
|
|
|
|
|
<P>The parameter "N" is required and its value is the number of table
|
|
|
|
|
entries that follow. Note that this may be different than the <I>N</I>
|
|
|
|
|
specified in the <A HREF = "angle_style.html">angle_style table</A> command. Let
|
|
|
|
|
Ntable = <I>N</I> in the angle_style command, and Nfile = "N" in the
|
|
|
|
|
tabulated file. What LAMMPS does is a preliminary interpolation by
|
|
|
|
|
creating splines using the Nfile tabulated values as nodal points. It
|
2010-11-18 00:26:24 +08:00
|
|
|
uses these to interpolate as needed to generate energy and derivative
|
2009-08-11 04:13:44 +08:00
|
|
|
values at Ntable different points. The resulting tables of length
|
|
|
|
|
Ntable are then used as described above, when computing energy and
|
2010-11-18 00:26:24 +08:00
|
|
|
force for individual angles and their atoms. This means that if you
|
|
|
|
|
want the interpolation tables of length Ntable to match exactly what
|
|
|
|
|
is in the tabulated file (with effectively no preliminary
|
|
|
|
|
interpolation), you should set Ntable = Nfile.
|
2009-08-11 04:13:44 +08:00
|
|
|
</P>
|
|
|
|
|
<P>The "FP" parameter is optional. If used, it is followed by two values
|
2010-11-18 00:26:24 +08:00
|
|
|
fplo and fphi, which are the 2nd derivatives at the innermost and
|
|
|
|
|
outermost angle settings. These values are needed by the spline
|
2009-08-11 04:13:44 +08:00
|
|
|
construction routines. If not specified by the "FP" parameter, they
|
2010-11-18 00:26:24 +08:00
|
|
|
are estimated (less accurately) by the first two and last two
|
|
|
|
|
derivative values in the table.
|
2009-08-11 04:13:44 +08:00
|
|
|
</P>
|
|
|
|
|
<P>The "EQ" parameter is also optional. If used, it is followed by a the
|
|
|
|
|
equilibrium angle value, which is used, for example, by the <A HREF = "fix_shake.html">fix
|
|
|
|
|
shake</A> command. If not used, the equilibrium angle is
|
|
|
|
|
set to 180.0.
|
|
|
|
|
</P>
|
|
|
|
|
<P>Following a blank line, the next N lines list the tabulated values.
|
|
|
|
|
On each line, the 1st value is the index from 1 to N, the 2nd value is
|
|
|
|
|
the angle value (in degrees), the 3rd value is the energy (in energy
|
2010-11-18 00:26:24 +08:00
|
|
|
units), and the 4th is -dE/d(theta) (also in energy units). The 3rd
|
|
|
|
|
term is the energy of the 3-atom configuration for the specified
|
|
|
|
|
angle. The last term is the derivative of the energy with respect to
|
|
|
|
|
the angle (in degrees, not radians). Thus the units of the last term
|
|
|
|
|
are still energy, not force. The angle values must increase from one
|
|
|
|
|
line to the next. The angle values must also begin with 0.0 and end
|
|
|
|
|
with 180.0, i.e. span the full range of possible angles.
|
2009-08-11 04:13:44 +08:00
|
|
|
</P>
|
|
|
|
|
<P>Note that one file can contain many sections, each with a tabulated
|
|
|
|
|
potential. LAMMPS reads the file section by section until it finds
|
|
|
|
|
one that matches the specified keyword.
|
|
|
|
|
</P>
|
|
|
|
|
<P><B>Restrictions:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<P>This angle style can only be used if LAMMPS was built with the
|
|
|
|
|
"molecular" package (which it is by default). See the <A HREF = "Section_start.html#2_3">Making
|
|
|
|
|
LAMMPS</A> section for more info on packages.
|
|
|
|
|
</P>
|
|
|
|
|
<P><B>Related commands:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<P><A HREF = "angle_coeff.html">angle_coeff</A>
|
|
|
|
|
</P>
|
|
|
|
|
<P><B>Default:</B> none
|
|
|
|
|
</P>
|
|
|
|
|
</HTML>
|
