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make computes rdf and adf error out multi cutoff neighbor lists if needed

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Axel Kohlmeyer
2024-03-03 12:27:39 -05:00
parent a776d8425f
commit 2809428fe2
6 changed files with 108 additions and 91 deletions
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37
doc/src/compute_rdf.rst
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@ -176,22 +176,29 @@ also numbers :math:`\ge 0.0`.
Restrictions
""""""""""""
The RDF is not computed for distances longer than the force cutoff,
since processors (in parallel) do not know about atom coordinates for
atoms further away than that distance. If you want an RDF for larger
distances, you can use the :doc:`rerun <rerun>` command to post-process
a dump file and set the cutoff for the potential to be longer in the
By default, the RDF is not computed for distances longer than the
largest force cutoff, since the neighbor list creation will only contain
pairs up to that distance (plus neighbor list skin). This distance can
be increased using the *cutoff* keyword but this keyword is only valid
with :doc:`neighbor styles 'bin' and 'nsq' <neighbor>`.
If you want an RDF for larger distances, you can also use the
:doc:`rerun <rerun>` command to post-process a dump file, use :doc:`pair
style zero <pair_zero>` and set the force cutoff to be longer in the
rerun script. Note that in the rerun context, the force cutoff is
arbitrary, since you are not running dynamics and thus are not changing
your model. The definition of :math:`g(r)` used by LAMMPS is only appropriate
for characterizing atoms that are uniformly distributed throughout the
simulation cell. In such cases, the coordination number is still
correct and meaningful. As an example, if a large simulation cell
contains only one atom of type *itypeN* and one of *jtypeN*, then :math:`g(r)`
will register an arbitrarily large spike at whatever distance they
happen to be at, and zero everywhere else.
The function :math:`\text{coord}(r)` will show a step
change from zero to one at the location of the spike in :math:`g(r)`.
arbitrary and with pair style zero you are not computing any forces, and
you are not running dynamics you are not changing the model that
generated the trajectory.
The definition of :math:`g(r)` used by LAMMPS is only appropriate for
characterizing atoms that are uniformly distributed throughout the
simulation cell. In such cases, the coordination number is still correct
and meaningful. As an example, if a large simulation cell contains only
one atom of type *itypeN* and one of *jtypeN*, then :math:`g(r)` will
register an arbitrarily large spike at whatever distance they happen to
be at, and zero everywhere else. The function :math:`\text{coord}(r)`
will show a step change from zero to one at the location of the spike in
:math:`g(r)`.
.. note::