forked from lijiext/lammps
122 lines
4.8 KiB
Plaintext
122 lines
4.8 KiB
Plaintext
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
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:link(lws,http://lammps.sandia.gov)
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:link(ld,Manual.html)
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:link(lc,Section_commands.html#comm)
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:line
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delete_bonds command :h3
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[Syntax:]
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delete_bonds group-ID style args keyword ... :pre
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group-ID = group ID :ulb,l
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style = {multi} or {atom} or {bond} or {angle} or {dihedral} or
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{improper} or {stats} :l
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{multi} args = none
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{atom} args = an atom type
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{bond} args = a bond type
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{angle} args = an angle type
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{dihedral} args = a dihedral type
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{improper} args = an improper type
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{stats} args = none :pre
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zero or more keywords may be appended to the args :l
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keyword = {undo} or {remove} or {special} :l
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:ule
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[Examples:]
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delete_bonds frozen multi remove
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delete_bonds all atom 4 special
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delete_bonds all stats :pre
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[Description:]
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Turn off (or on) molecular topology interactions, i.e. bonds, angles,
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dihedrals, impropers. This command is useful for deleting
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interactions that have been previously turned off by bond-breaking
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potentials. It is also useful for turning off topology interactions
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between frozen or rigid atoms. Pairwise interactions can be turned
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off via the "neigh_modify exclude"_neigh_modify.html command. The
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"fix shake"_fix_shake.html command also effectively turns off certain
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bond and angle interactions.
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For all styles, an interaction is only turned off (or on) if all the
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atoms involved are in the specified group. For style {multi} this is
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the only criterion applied - all types of bonds, angles, dihedrals,
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impropers in the group turned off.
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For style {atom}, one or more of the atoms involved must also be of
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the specified type. For style {bond}, only bonds are candidates for
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turn-off, and the bond must be of the specified type. Styles {angle},
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{dihedral}, and {improper} are treated similarly.
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For style {bond}, you can set the type to 0 to delete bonds that have
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been previously broken; e.g. see the "bond_style
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quartic"_bond_style.html command.
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For style {stats} no interactions are turned off (or on); the status
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of all interactions in the specified group is simply reported. This
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is useful for diagnostic purposes if bonds have been turned off by a
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bond-breaking potential during a previous run.
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The default behavior of the delete_bonds command is to turn off
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interactions by toggling their type to a negative value. E.g. a
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bond_type of 2 is set to -2. The neighbor list creation routines will
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not include such an interaction in their interaction lists. The
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default is also to not alter the list of 1-2, 1-3, 1-4 neighbors
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computed by the "special_bonds"_special_bonds.html command and used to
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weight pairwise force and energy calculations. This means that
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pairwise computations will proceed as if the bond (or angle, etc) were
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still turned on.
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The keywords listed above can be appended to the argument list to
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alter the default behavior.
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The {undo} keyword inverts the delete_bonds command so that the
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specified bonds, angles, etc are turned on if they are currently
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turned off. This means any negative value is toggled to positive.
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Note that the "fix shake"_fix_shake.html command also sets bond and
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angle types negative, so this option should not be used on those
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interactions.
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The {remove} keyword is invoked at the end of the delete_bonds
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operation. It causes turned-off bonds (angles, etc) to be removed
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from each atom's data structure and then adjusts the global bond
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(angle, etc) counts accordingly. Removal is a permanent change;
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removed bonds cannot be turned back on via the {undo} keyword.
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Removal does not alter the pairwise 1-2, 1-3, 1-4 weighting list.
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The {special} keyword is invoked at the end of the delete_bonds
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operation, after (optional) removal. It re-computes the pairwise 1-2,
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1-3, 1-4 weighting list. The weighting list computation treats
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turned-off bonds the same as turned-on. Thus, turned-off bonds must
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be removed if you wish to change the weighting list.
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Note that the choice of {remove} and {special} options affects how
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1-2, 1-3, 1-4 pairwise interactions will be computed across bonds that
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have been modified by the delete_bonds command.
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[Restrictions:]
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This command requires inter-processor communication to coordinate the
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deleting of bonds. This means that your system must be ready to
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perform a simulation before using this command (force fields setup,
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atom masses set, etc).
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If deleted bonds (angles, etc) are removed but the 1-2, 1-3, 1-4
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weighting list is not recomputed, this can cause a later "fix
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shake"_fix_shake.html command to fail due to an atom's bonds being
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inconsistent with the weighting list. This should only happen if the
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group used in the fix command includes both atoms in the bond, in
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which case you probably should be recomputing the weighting list.
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[Related commands:]
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"neigh_modify"_neigh_modify.html exclude,
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"special_bonds"_special_bonds.html, "fix shake"_fix_shake.html
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[Default:] none
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