# bond_write command

## Syntax

``` LAMMPS
bond_write btype N inner outer file keyword itype jtype
```

-   btype = bond type
-   N = \# of values
-   inner,outer = inner and outer bond length (distance units)
-   file = name of file to write values to
-   keyword = section name in file for this set of tabulated values
-   itype,jtype = 2 atom types (optional)

## Examples

``` LAMMPS
bond_write 1 500 0.5 3.5 table.txt Harmonic_1
bond_write 3 1000 0.1 6.0 table.txt Morse
```

## Description

Write energy and force values to a file as a function of distance for
the currently defined [bond style](bond_style) for a selected bond type.
This is useful for plotting the potential function or otherwise
debugging its values. The resulting file can also be used as input for
use with [bond style table](bond_table).

If the file already exists, the table of values is appended to the end
of the file to allow multiple tables of energy and force to be included
in one file. The individual sections may be identified by the *keyword*.

The energy and force values are computed at distances from *inner* to
*outer* for 2 interacting atoms forming a bond of type *btype*, using
the appropriate [bond_coeff](bond_coeff) coefficients. N evenly spaced
distances are used.

For example, for N = 7, inner = 1.0, and outer = 4.0, values are
computed at r = 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0.

The file is written in the format used as input for the [bond_style
table](bond_table) option with *keyword* as the section name. Each line
written to the file lists an index number (1-N), a distance (in distance
units), an energy (in energy units), and a force (in force units). In
case a new file is created, the first line will be a comment with a
\"DATE:\" and \"UNITS:\" tag with the current date and [units](units)
settings. For subsequent invocations of the *bond_write* command for the
same file, data will be appended and the current units settings will be
compared to the data from the header, if present. The *bond_write*
command will refuse to add a table to an existing file if the units are
not the same.

## Restrictions

All force field coefficients for bond and other kinds of interactions
must be set before this command can be invoked.

Due to how the bond force is computed, an inner value \> 0.0 must be
specified even if the potential has a finite value at r = 0.0.

## Related commands

[bond_style table](bond_table), [angle_write](angle_write),
[bond_style](bond_style), [bond_coeff](bond_coeff)

## Default

none