.. _vib_freq:

*********************
Vibrational Frequency
*********************

.. note:: The scripts for this step of the tutorial can be found in ``chemsh/6_mgo+co2_vib/``

The script ``mgoco2.py`` demonstrates how the vibrational frequency of 
CO\ :sub:`2` can be calculated. This is a very similar setup to the MgO-CO\ :sub:`2` 
geometry optimisation, but starts from the final optimised energy. 
The active region is also reduced to the CO\ :sub:`2` 
atoms only, in order to reduce the size of the Hessian matrix required:

.. literalinclude:: ../../samples/mgo_surface/6_mgo+co2_vib/mgoco2.py
    :lines: 20-21

DL-FIND is used to run the vibrational analysis, which is specified 
using the ``thermal=True`` option in the ``Opt()`` specification:

.. literalinclude:: ../../samples/mgo_surface/6_mgo+co2_vib/mgoco2.py
    :lines: 41-43