Page Menu
Home
c4science
Search
Configure Global Search
Log In
Files
F90542220
bond_style_quartic.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, Nov 2, 14:51
Size
3 KB
Mime Type
text/html
Expires
Mon, Nov 4, 14:51 (1 d, 23 h)
Engine
blob
Format
Raw Data
Handle
22037248
Attached To
rLAMMPS lammps
bond_style_quartic.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>bond_style quartic command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>bond_style quartic
</PRE>
<P><B>Examples:</B>
</P>
<PRE>bond_style quartic
bond_coeff 2 1200 -0.55 0.25 1.3 34.6878
</PRE>
<P><B>Description:</B>
</P>
<P>The <I>quartic</I> bond style uses the potential
</P>
<CENTER><IMG SRC = "Eqs/bond_quartic.jpg">
</CENTER>
<P>to define a bond that can be broken as the simulation proceeds (e.g.
due to a polymer being stretched). The sigma and epsilon used in the
LJ portion of the formula are both set equal to 1.0 by LAMMPS.
</P>
<P>The following coefficients must be defined for each bond type via the
<A HREF = "bond_coeff.html">bond_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>K (energy/distance^2)
<LI>B1 (distance)
<LI>B2 (distance)
<LI>Rc (distance)
<LI>U0 (energy)
</UL>
<P>This potential was constructed to mimic the FENE bond potential for
coarse-grained polymer chains. When monomers with sigma = epsilon =
1.0 are used, the following choice of parameters gives a quartic
potential that looks nearly like the FENE potential: K = 1200, B1 =
-0.55, B2 = 0.25, Rc = 1.3, and U0 = 34.6878. Different parameters
can be specified using the <A HREF = "bond_coeff.html">bond_coeff</A> command, but
you will need to choose them carefully so they form a suitable bond
potential.
</P>
<P>Rc is the cutoff length at which the bond potential goes smoothly to a
local maximium. If a bond length ever becomes > Rc, LAMMPS "breaks"
the bond, which means two things. First, the bond potential is turned
off by setting its type to 0, and is no longer computed. Second, a
pairwise interaction between the two atoms is turned on, since they
are no longer bonded.
</P>
<P>LAMMPS does the second task via a computational sleight-of-hand. It
subtracts the pairwise interaction as part of the bond computation.
When the bond breaks, the subtraction stops. For this to work, the
pairwise interaction must always be computed by the
<A HREF = "pair_style.html">pair_style</A> command, whether the bond is broken or
not. This means that <A HREF = "special_bonds.html">special_bonds</A> must be set
to 1,1,1, as indicated as a restriction below.
</P>
<P>Note that when bonds are dumped to a file via <A HREF = "dump.html">dump bond</A>,
bonds with type 0 are not included. The
<A HREF = "delete_bonds.html">delete_bonds</A> command can also be used to query the
status of broken bonds or permanently delete them, e.g.:
</P>
<PRE>delete_bonds all stats
delete_bonds all bond 0 remove
</PRE>
<P><B>Restrictions:</B>
</P>
<P>The <I>quartic</I> style requires that <A HREF = "special_bonds.html">special_bonds</A>
parameters be set to 1,1,1. Three- and four-body interactions (angle,
dihedral, etc) cannot be used with <I>quartic</I> bonds.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "bond_coeff.html">bond_coeff</A>, <A HREF = "delete_bonds.html">delete_bonds</A>
</P>
<P><B>Default:</B> none
</P>
</HTML>
Event Timeline
Log In to Comment