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improper_style_class2.html
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Tue, Nov 26, 10:41
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rLAMMPS lammps
improper_style_class2.html
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<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>
improper_style class2 command
</H3>
<P><B>
Syntax:
</B>
</P>
<PRE>
improper_style class2
</PRE>
<P><B>
Examples:
</B>
</P>
<PRE>
improper_style class2
improper_coeff 1 100.0 0
</PRE>
<P><B>
Description:
</B>
</P>
<P>
The
<I>
class2
</I>
improper style uses the potential
</P>
<CENTER><IMG
SRC =
"Eqs/improper_class2.jpg"
>
</CENTER>
<P>
where Ei is the improper term and Eaa is an angle-angle term. The chi
used in Ei is an average over 3 possible chi orientations. The
subscripts on the various theta's refer to different combinations of
atoms i,j,k,l used to form the angle; theta1, theta2, theta3 are the
equilibrium positions of those angles.
</P>
<P>
See
<A
HREF =
"#Sun"
>
(Sun)
</A>
for a description of the COMPASS class2 force field.
</P>
<P>
The following coefficients must be defined for each improper type via the
<A
HREF =
"improper_coeff.html"
>
improper_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>
<P>
For this style, only coefficients for the Ei formula can be specified
in the input script. These are the 2 coefficients:
</P>
<UL><LI>
K (energy/radian^2)
<LI>
X0 (degrees)
</UL>
<P>
X0 is specified in degrees, but LAMMPS converts it to radians
internally; hence the units of K are in energy/radian^2.
</P>
<P>
Coefficients for the Eaa formula must be specified in the data file.
For the Eaa formula, the coefficients are listed under a
"AngleAngle Coeffs" heading and each line lists 6 coefficients:
</P>
<UL><LI>
M1 (energy/distance)
<LI>
M2 (energy/distance)
<LI>
M3 (energy/distance)
<LI>
theta1 (degrees)
<LI>
theta2 (degrees)
<LI>
theta3 (degrees)
</UL>
<P>
The theta values are specified in degrees, but LAMMPS converts them to
radians internally; hence the units of M are in energy/radian^2.
</P>
<P><B>
Restrictions:
</B>
</P>
<P>
This improper style is part of the "class2" package. It is only
enabled if LAMMPS was built with that package. See the
<A
HREF =
"Section_start.html#2_2"
>
Making
LAMMPS
</A>
section for more info.
</P>
<P><B>
Related commands:
</B>
</P>
<P><A
HREF =
"improper_coeff.html"
>
improper_coeff
</A>
</P>
<P><B>
Default:
</B>
none
</P>
<HR>
<A
NAME =
"Sun"
></A>
<P><B>
(Sun)
</B>
Sun, J Phys Chem B 102, 7338-7364 (1998).
</P>
</HTML>
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