# bond_style command

## Syntax

``` LAMMPS
bond_style style args
```

-   style = *none* or *zero* or *hybrid* or *bpm/rotational* or
    *bpm/spring* or *class2* or *fene* or *fene/expand* or *fene/nm* or
    *gaussian* or *gromos* or *harmonic* or *harmonic/restrain*
    *harmonic/shift* or *harmonic/shift/cut* or *lepton* or *morse* or
    *nonlinear* or *oxdna/fene* or *oxdena2/fene* or *oxrna2/fene* or
    *quartic* or *special* or *table*
-   args = none for any style except *hybrid*
    -   *hybrid* args = list of one or more styles

## Examples

``` LAMMPS
bond_style harmonic
bond_style fene
bond_style hybrid harmonic fene
```

## 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) command. Bonds are
defined between specified pairs of atoms and remain in force for the
duration of the simulation (unless new bonds are created or existing
bonds break, which is possible in some fixes and bond potentials). The
list of bonded atoms is read in by a [read_data](read_data) or
[read_restart](read_restart) command from a data or restart file. By
contrast, pair potentials are typically defined between all pairs of
atoms within a cutoff distance and the set of active interactions
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) command.

All bond potentials store their coefficient data in binary restart files
which means bond_style and [bond_coeff](bond_coeff) commands do not need
to be re-specified in an input script that restarts a simulation. See
the [read_restart](read_restart) command for details on how to do this.
The one exception is that bond_style *hybrid* only stores the list of
sub-styles in the restart file; bond coefficients need to be
re-specified.

:::: note
::: title
Note
:::

When both a bond and pair style is defined, the
[special_bonds](special_bonds) command often needs to be used to turn
off (or weight) the pairwise interaction that would otherwise exist
between 2 bonded atoms.
::::

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

------------------------------------------------------------------------

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) command.

Click on the style to display the formula it computes, any additional
arguments specified in the bond_style command, and coefficients
specified by the associated [bond_coeff](bond_coeff) command.

There are also additional accelerated pair styles included in the LAMMPS
distribution for faster performance on CPUs, GPUs, and KNLs. The
individual style names on the [Commands bond](Commands_bond) doc page
are followed by one or more of (g,i,k,o,t) to indicate which accelerated
styles exist.

-   [none](bond_none) - turn off bonded interactions
-   [zero](bond_zero) - topology but no interactions
-   [hybrid](bond_hybrid) - define multiple styles of bond interactions
-   [bpm/rotational](bond_bpm_rotational) - breakable bond with forces
    and torques based on deviation from reference state
-   [bpm/spring](bond_bpm_spring) - breakable bond with forces based on
    deviation from reference length
-   [class2](bond_class2) - COMPASS (class 2) bond
-   [fene](bond_fene) - FENE (finite-extensible non-linear elastic) bond
-   [fene/expand](bond_fene_expand) - FENE bonds with variable size
    particles
-   [fene/nm](bond_fene) - FENE bonds with a generalized Lennard-Jones
    potential
-   [gaussian](bond_gaussian) - multicentered Gaussian-based bond
    potential
-   [gromos](bond_gromos) - GROMOS force field bond
-   [harmonic](bond_harmonic) - harmonic bond
-   [harmonic/restrain](bond_harmonic_restrain) - harmonic bond to
    restrain to original bond distance
-   [harmonic/shift](bond_harmonic_shift) - shifted harmonic bond
-   [harmonic/shift/cut](bond_harmonic_shift_cut) - shifted harmonic
    bond with a cutoff
-   [lepton](bond_lepton) - bond potential from evaluating a string
-   [mesocnt](bond_mesocnt) - Harmonic bond wrapper with
    parameterization presets for nanotubes
-   [mm3](bond_mm3) - MM3 anharmonic bond
-   [morse](bond_morse) - Morse bond
-   [nonlinear](bond_nonlinear) - nonlinear bond
-   [oxdna/fene](bond_oxdna) - modified FENE bond suitable for DNA
    modeling
-   [oxdna2/fene](bond_oxdna) - same as oxdna but used with different
    pair styles
-   [oxrna2/fene](bond_oxdna) - modified FENE bond suitable for RNA
    modeling
-   [quartic](bond_quartic) - breakable quartic bond
-   [special](bond_special) - enable special bond exclusions for 1-5
    pairs and beyond
-   [table](bond_table) - tabulated by bond length

------------------------------------------------------------------------

## Restrictions

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

Most bond styles are part of the MOLECULE package. They are only enabled
if LAMMPS was built with that package. See the [Build
package](Build_package) page for more info. The doc pages for individual
bond potentials tell if it is part of a package.

## Related commands

[bond_coeff](bond_coeff), [delete_bonds](delete_bonds)

## Default

``` LAMMPS
bond_style none
```