<HTML> <CENTER><A HREF = "http://www.cfdem.com">LIGGGHTS(R)-PUBLIC WWW Site</A> - <A HREF = "Manual.html">LIGGGHTS(R)-PUBLIC Documentation</A> - <A HREF = "Section_commands.html#comm">LIGGGHTS(R)-PUBLIC Commands</A> </CENTER> <HR> <H3>delete_bonds command </H3> <P><B>Syntax:</B> </P> <PRE>delete_bonds group-ID style args keyword ... </PRE> <UL><LI>group-ID = group ID <LI>style = <I>multi</I> or <I>atom</I> or <I>bond</I> or <I>stats</I> <PRE> <I>multi</I> args = none <I>atom</I> args = an atom type <I>bond</I> args = a bond type <I>stats</I> args = none </PRE> <LI>zero or more keywords may be appended <LI>keyword = <I>any</I> or <I>undo</I> or <I>remove</I> or <I>special</I> </UL> <P><B>Examples:</B> </P> <PRE>delete_bonds frozen multi remove delete_bonds all atom 4 special delete_bonds all stats </PRE> <P><B>Description:</B> </P> <P>Turn off (or on) molecular topology interactions, i.e. bonds. This command is useful for deleting interactions that have been previously turned off by bond-breaking potentials. It is also useful for turning off topology interactions between frozen or rigid atoms. Pairwise interactions can be turned off via the <A HREF = "neigh_modify.html">neigh_modify exclude</A> command. </P> <P>For all styles, by default, an interaction is only turned off (or on) if all the atoms involved are in the specified group. See the <I>any</I> keyword to change the behavior. </P> <P>Style <I>atom</I> is the same as style <I>multi</I> except that in addition, one or more of the atoms involved in the bond, interaction must also be of the specified atom type. </P> <P>For style <I>bond</I>, only bonds are candidates for turn-off, and the bond must also be of the specified type. </P> <P>For style <I>bond</I>, you can set the type to 0 to delete bonds that have been previously broken by a bond-breaking potential (which sets the bond type to 0 when a bond is broken); e.g. see the <A HREF = "bond_style.html">bond_style quartic</A> command. </P> <P>For style <I>stats</I> no interactions are turned off (or on); the status of all interactions in the specified group is simply reported. This is useful for diagnostic purposes if bonds have been turned off by a bond-breaking potential during a previous run. </P> <P>The default behavior of the delete_bonds command is to turn off interactions by toggling their type to a negative value, but not to permanently remove the interaction. E.g. a bond_type of 2 is set to -2. The neighbor list creation routines will not include such an interaction in their interaction lists. The default is also to not alter the list of 1-2, 1-3, 1-4 neighbors computed by the <A HREF = "special_bonds.html">special_bonds</A> command and used to weight pairwise force and energy calculations. This means that pairwise computations will proceed as if the bond were still turned on. </P> <P>Several keywords can be appended to the argument list to alter the default behaviors. </P> <P>The <I>any</I> keyword changes the requirement that all atoms in the bond must be in the specified group in order to turn-off the interaction. Instead, if any of the atoms in the interaction are in the specified group, it will be turned off (or on if the <I>undo</I> keyword is used). </P> <P>The <I>undo</I> keyword inverts the delete_bonds command so that the specified bonds are turned on if they are currently turned off. </P> <P>The <I>remove</I> keyword is invoked at the end of the delete_bonds operation. It causes turned-off bonds to be removed from each atom's data structure and then adjusts the global bond counts accordingly. Removal is a permanent change; removed bonds cannot be turned back on via the <I>undo</I> keyword. Removal does not alter the pairwise 1-2, 1-3, 1-4 weighting list. </P> <P>The <I>special</I> keyword is invoked at the end of the delete_bonds operation, after (optional) removal. It re-computes the pairwise 1-2, 1-3, 1-4 weighting list. The weighting list computation treats turned-off bonds the same as turned-on. Thus, turned-off bonds must be removed if you wish to change the weighting list. </P> <P>Note that the choice of <I>remove</I> and <I>special</I> options affects how 1-2, 1-3, 1-4 pairwise interactions will be computed across bonds that have been modified by the delete_bonds command. </P> <P><B>Restrictions:</B> </P> <P>This command requires inter-processor communication to coordinate the deleting of bonds. This means that your system must be ready to perform a simulation before using this command (force fields setup, atom masses set, etc). </P> <P><B>Related commands:</B> </P> <P><A HREF = "neigh_modify.html">neigh_modify</A> exclude, <A HREF = "special_bonds.html">special_bonds</A> </P> <P><B>Default:</B> none </P> </HTML>