.. index:: bond_write

bond_write command
==================

Syntax
""""""

.. code-block:: 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 = two atom types (optional)

Examples
""""""""

.. code-block:: 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 :doc:`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 :doc:`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 two interacting atoms forming a bond of type *btype*, using
the appropriate :doc:`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 :doc:`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 :doc:`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
""""""""""""""""

:doc:`bond_style table <bond_table>`, :doc:`angle_write <angle_write>`,
:doc:`bond_style <bond_style>`, :doc:`bond_coeff <bond_coeff>`

Default
"""""""

none
