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Stan Gerald Moore
2021-09-14 10:45:45 -06:00
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doc/src/fix_acks2_reaxff.rst
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@ -1,8 +1,12 @@
.. index:: fix acks2/reaxff
.. index:: fix acks2/reaxff/kk
fix acks2/reaxff command
====================
Accelerator Variants: *acks2/reaxff/kk*
Syntax
""""""
@ -12,7 +16,7 @@ Syntax
* ID, group-ID are documented in :doc:`fix <fix>` command
* acks2/reaxff = style name of this fix command
* Nevery = perform QEq every this many steps
* Nevery = perform ACKS2 every this many steps
* cutlo,cuthi = lo and hi cutoff for Taper radius
* tolerance = precision to which charges will be equilibrated
* params = reaxff or a filename
@ -28,24 +32,28 @@ Examples
Description
"""""""""""
Perform the charge equilibration (QEq) method as described in :ref:`(Verstraelen) <Verstraelen>`. It is
typically used in conjunction with the ReaxFF force field model as
Perform the atom-condensed Kohn-Sham DFT to second order (ACKS2) charge
equilibration method as described in :ref:`(Verstraelen) <Verstraelen>`.
ACKS2 impedes unphysical long-range charge transfer sometimes seen with
QEq (e.g. for dissociation of molecules), at increased computational cost.
It is typically used in conjunction with the ReaxFF force field model as
implemented in the :doc:`pair_style reaxff <pair_reaxff>` command, but
it can be used with any potential in LAMMPS, so long as it defines and
uses charges on each atom. For more technical details about the
charge equilibration performed by fix acks2/reaxff, see the
:ref:`(O'Hearn) <O'Hearn>` paper.
:ref:`(O'Hearn) <O'Hearn>` paper.
The QEq method minimizes the electrostatic energy of the system by
The ACKS2 method minimizes the electrostatic energy of the system by
adjusting the partial charge on individual atoms based on interactions
with their neighbors. It requires some parameters for each atom type.
with their neighbors. It requires some parameters
for each atom type.
If the *params* setting above is the word "reaxff", then these are
extracted from the :doc:`pair_style reaxff <pair_reaxff>` command and
the ReaxFF force field file it reads in. If a file name is specified
for *params*\ , then the parameters are taken from the specified file
and the file must contain one line for each atom type. The latter
form must be used when performing QeQ with a non-ReaxFF potential.
Each line should be formatted as follows:
The lines should be formatted as follows:
.. parsed-literal::
@ -69,6 +77,12 @@ with the *start/stop* keywords of the :doc:`run <run>` command.
This fix is invoked during :doc:`energy minimization <minimize>`.
----------
.. include:: accel_styles.rst
----------
Restrictions
""""""""""""
@ -82,7 +96,7 @@ be used for periodic cell dimensions less than 10 angstroms.
Related commands
""""""""""""""""
:doc:`pair_style reaxff <pair_reaxff>`
:doc:`pair_style reaxff <pair_reaxff>`, :doc:`fix qeq/reaxff <fix_qeq_reaxff>`
**Default:** none