lammps/doc/bond_style.txt

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bond_style command :h3

[Syntax:]

bond_style style args :pre

style = {none} or {hybrid} or {class2} or {fene} or {fene/expand} or \
        {harmonic} or {morse} or {nonlinear} or {quartic} :ul
  args = none for any style except {hybrid}
  {hybrid} args = list of one or more styles :pre

[Examples:]

bond_style harmonic
bond_style fene
bond_style hybrid harmonic fene :pre

[Description:]

Set the formula(s) LAMMPS uses to compute bond interactions between
pairs of atoms.  In LAMMPS, a bond differs from a pairwise
interaction, which are set via the "pair_style"_pair_style.html
command.  Bonds are defined between specified pairs of atoms and
remain in force for the duration of the simulation (unless the bond
breaks which is possible in some bond potentials).  The list of bonded
atoms is read in by a "read_data"_read_data.html or
"read_restart"_read_restart.html command from a data or restart file.
By contrast, pair potentials are defined between pairs of atoms that
are within a cutoff distance and the set of active interactions
typically changes over time.

Hybrid models where bonds are computed using different bond potentials
can be setup using the {hybrid} bond style.

The coefficients associated with a bond style can be specified in a
data or restart file or via the "bond_coeff"_bond_coeff.html command.

In the formulas listed for each bond style, {r} is the distance
between the 2 atoms in the bond.

Note that when both a bond and pair style is defined, the
"special_bonds"_special_bonds.html command often needs to be used to
turn off (or weight) the pairwise interaction that would otherwise
exist between 2 bonded atoms.

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Here is an alphabetic list of bond styles defined in LAMMPS.  Click on
the style to display the formula it computes and coefficients
specified by the associated "bond_coeff"_bond_coeff.html command:

"bond_style none"_bond_none.html - turn off bonded interactions
"bond_style hybrid"_bond_hybrid.html - define multiple styles of bond interactions :ul

"bond_style class2"_bond_class2.html - COMPASS (class 2) bond
"bond_style fene"_bond_fene.html - FENE (finite-extensible non-linear elastic) bond
"bond_style fene/expand"_bond_fene_expand.html - FENE bonds with variable size particles
"bond_style harmonic"_bond_harmonic.html - harmonic bond
"bond_style morse"_bond_morse.html - Morse bond
"bond_style nonlinear"_bond_nonlinear.html - nonlinear bond
"bond_style quartic"_bond_quartic.html - breakable quartic bond :ul

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[Restrictions:]

Bond styles can only be set for atom styles that allow bonds to be
defined.

Bond styles are part of the "molecular" package or other packages as
noted in their documentation.  They are only enabled if LAMMPS was
built with that package.  See the "Making
LAMMPS"_Section_start.html#2_2 section for more info.

[Related commands:]

"bond_coeff"_bond_coeff.html, "delete_bonds"_delete_bonds.html

[Default:]

bond_style none