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.. _structure_optimization:
========================
Structure optimization
========================
In the tutorial on :ref:`how to calculate atomization energies
<atomization_energy>`, we calculated the atomization energy for
`\rm{H}_2` using the experimental bond length of 0.74 Å. In
this tutorial, we ask an :mod:`ASE optimizer <ase.optimize>`
to iteratively find
the structural energy minimum, where all atomic forces are below 0.05
eV/Å. The following script will do the job:
.. literalinclude:: relax.py
The result is:
.. literalinclude:: optimization.txt
.. note::
You must run the :ref:`atomization <atomization_energy>` script first.
To save time you could have told the minimizer to keep one atom fixed,
and only relaxing the other. This is achieved through the use of
constraints::
molecule.set_constraint(FixAtoms(mask=[0, 1]))
The keyword ``mask`` contains list of booleans for each atom indicating
whether the atom's position should be fixed or not. See the
:mod:`ase.constraints` module on the ASE page for
more information and examples for setting constraints.
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