document the use and generation of "DATE:" and "UNITS:" tags

:doc:`bond_style <bond_style>` *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).

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, and bond_write will refuse to add a table if the units are not

the same.

Restrictions

""""""""""""

of the distribution.  For some potentials, such as EAM, other archives

of suitable files can be found on the Web.  They can be used with

LAMMPS so long as they are in the format LAMMPS expects, as discussed

on the individual doc pages.

on the individual doc pages.  The first line of potential files may

contain metadata with upper case tags followed their value. These may

be parsed and used by LAMMPS.  Currently supported are the "DATE:"

tag and the "UNITS:" tag.  For pair styles that have been programmed

to support the metadata, the value of the "DATE:" tag is printed to

the screen and logfile so that the version of a potential file can be

later identified.  The "UNITS:" tag indicates the :doc:`units <units>`

setting required for this particular potential file.  If the potential

file ware created for a different sets of units, LAMMPS will terminate

with an error.  If the potential file does not contain the tag, no

check will be made.

When a pair_coeff command using a potential file is specified, LAMMPS

looks for the potential file in 2 places.  First it looks in the

----------

The format of a tabulated file is a series of one or more sections,

defined as follows (without the parenthesized comments):

The format of a tabulated file has an (optional) header followed by a

series of one or more sections, defined as follows (without the

parenthesized comments). The header must start with a `#` character

and the DATE: and UNITS: tags will be parsed and used:

.. parsed-literal::

   # DATE: 2020-06-10  UNITS: real  CONTRIBUTOR: ... (header line)

   # Morse potential for Fe   (one or more comment or blank lines)

   MORSE_FE                   (keyword is first text on line)

potential function or otherwise debugging its values.  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.

file.  In case a new file is created, the first line will be a comment

containing a "DATE:" and "UNITS:" tag with the current date and the

current :doc:`units <units>` setting as argument.  For subsequent

invocations of the pair_write command, the current units setting is

compared against the entry in the file, if present, and pair_write

will refuse to add a table if the units are not the same.

The energy and force values are computed at distances from inner to

outer for 2 interacting atoms of type itype and jtype, using the