# newton command

## Syntax

    newton flag
    newton flag1 flag2

-   flag = *on* or *off* for both pairwise and bonded interactions
-   flag1 = *on* or *off* for pairwise interactions
-   flag2 = *on* or *off* for bonded interactions

## Examples

``` LAMMPS
newton off
newton on off
```

## Description

This command turns Newton\'s third law *on* or *off* for pairwise and
bonded interactions. For most problems, setting Newton\'s third law to
*on* means a modest savings in computation at the cost of two times more
communication. Whether this is faster depends on problem size, force
cutoff lengths, a machine\'s compute/communication ratio, and how many
processors are being used.

Setting the pairwise newton flag to *off* means that if two interacting
atoms are on different processors, both processors compute their
interaction and the resulting force information is not communicated.
Similarly, for bonded interactions, newton *off* means that if a bond,
angle, dihedral, or improper interaction contains atoms on 2 or more
processors, the interaction is computed by each processor.

LAMMPS should produce the same answers for any newton flag settings,
except for round-off issues.

With [run_style](run_style) *respa* and only bonded interactions (bond,
angle, etc) computed in the innermost timestep, it may be faster to turn
newton *off* for bonded interactions, to avoid extra communication in
the innermost loop.

## Restrictions

The newton bond setting cannot be changed after the simulation box is
defined by a [read_data](read_data) or [create_box](create_box) command.

## Related commands

[run_style](run_style) respa

## Default

``` LAMMPS
newton on
```