
.. _recycling:

=========
Recycling
=========

We have developed a method of saddle point recycling that can significantly 
reduce the computational cost of the AKMC algorithm. [#xu08_114104]_

Suppose we are in reactant state :math:`R_0`, and we have discovered a series of
saddles and their corresponding products, :math:`S_i` and :math:`P_i`, respectively.  Once
we have reached confidence that we have found all energetically
relevant processes, we select one of these processes and move to the
corresponding product state.  For this example, let us assume that we have selected
the process with saddle :math:`S_0` and product :math:`P_0`.  If we have found :math:`N`
energetically relevant processes in state :math:`R_0`, we can make suggestions
of the saddle geometries :math:`G_i` for saddles leading out of state :math:`P_0`

:math:`G_i = P_0 + (S_i - R_0)`

We use a min-mode following algorithm to converge these suggested saddle points.
To reach confidence again in state :math:`P_0`, we need only perform saddle searches
in the region around the atoms that moved significantly from state :math:`R_0` to
state :math:`P_0`, resulting in a significant reduction in computational costs.  If this region
is local, the overall cost does not increase with the total system size.

[Recycling] Options
===================

**use_recycling**: Turn recycling on and off.

    default: ``False``

**move_distance**: The distance an atom must move to be considered in the "hole".

    default: ``0.2``

**displace_moved_only**: When performing saddle search displacements, only use atoms in the vicinty of the hole as displacement epicenters.

    default: ``False``

**save_suggestions**: If true, the suggestions made by saddle recycling are saved to the "saddle_suggestions" directory of the state directory for which the saddles are being suggested.

    default: ``False``


.. rubric:: References

.. [#xu08_114104] L. Xu and G. Henkelman, "Adaptive kinetic Monte Carlo for first-principles accelerated dynamics" *J. Chem. Phys.* **129**, 114104 (2008).  doi:`10.1063/1.2976010 <http://dx.doi.org/10.1063/1.2976010>`_

