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.. _constraints diffusion tutorial:
=======================================================
Surface diffusion energy barriers using ASE constraints
=======================================================
In this tutorial, we will calculate the energy barrier that was found
using the :mod:`NEB <ase.mep.neb>` method in the :ref:`diffusion tutorial`
tutorial. Here, we use a simple :class:`~ase.constraints.FixedPlane`
constraint that forces the Au atom to relax in the *yz*-plane only:
.. literalinclude:: diffusion4.py
The result can be analysed with the command :command:`ase gui mep?.traj -n
-1` (choose :menuselection:`Tools --> NEB`). The barrier is found to
be 0.35 eV - exactly as in the :ref:`NEB <diffusion tutorial>`
tutorial.
Here is a side-view of the path (unit cell repeated twice):
.. image:: diffusion-path.png
.. seealso::
* :mod:`ase.mep.neb`
* :mod:`ase.constraints`
* :ref:`diffusion tutorial`
* :func:`~ase.build.fcc100`
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