Page Menu
Home
c4science
Search
Configure Global Search
Log In
Files
F111552754
improper_class2.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, May 3, 05:47
Size
3 KB
Mime Type
text/html
Expires
Mon, May 5, 05:47 (2 d)
Engine
blob
Format
Raw Data
Handle
25935203
Attached To
rLAMMPS lammps
improper_class2.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>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 3 X
terms used in Ei are an average over the 3 out-of-plane angles.
</P>
<P>The 4 atoms in an improper quadruplet (listed in the data file read by
the <A HREF = "read_data.html">read_data</A> command) are ordered I,J,K,L. X_IJKL
refers to the angle between the plane of I,J,K and the plane of J,K,L,
and the bond JK lies in both planes. Similarly for X_KJLI and X_LJIK.
Note that atom J appears in the common bonds (JI, JK, JL) of all 3 X
terms. Thus J (the 2nd atom in the quadruplet) is the atom of
symmetry in this formulation.
</P>
<P>The subscripts on the various theta's refer to different combinations
of 3 atoms (I,J,K,L) used to form a particular angle. E.g. Theta_IJL
is the angle formed by atoms I,J,L with J in the middle. 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, coefficients for the Ei formula can be specified in
eiher the input script or data file. 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 can only 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 can only be used if LAMMPS was built with the
"class2" package. 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 = "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>
Event Timeline
Log In to Comment