opt
======

This option controls the geometry optimization details.

.. contents::
   :local:

.. option:: num_steps

   .. list-table::
      :stub-columns: 1
      :widths: 5 20
   
      * - Value
        - An integer
      * - Default
        - ``1000``
   
   The maximum number of geometry optimization steps.

.. option:: epsilon

   .. list-table::
      :stub-columns: 1
      :widths: 5 20
   
      * - Value
        - A real number
      * - Default
        - ``1.E-5``
   
   The l-BFGS convergence condition. If the ratio of gradient norm to coordinate norm is less than ``epsilon``, then the optimization is assumed to be converged. This only works if l-BFGS is used.

   .. option:: grad_cov

   .. list-table::
      :stub-columns: 1
      :widths: 5 20
   
      * - Value
        - A real number 
      * - Default
        - ``1.E-3``

  The gradient convergence threshold. When ``grad_cov`` and ``dr_cov`` are both met, the optimized structure will be set to be converged.

.. option:: dr_cov

   .. list-table::
      :stub-columns: 1
      :widths: 5 20
   
      * - Value
        - A real number 
      * - Default
        - ``1.E-3``

  The displacement convergence threshold. When ``grad_cov`` and ``dr_cov`` are both met, the optimized structure will be set to be converged.

.. option:: fix_atoms

   .. list-table::
      :stub-columns: 1
      :widths: 5 20
   
      * - Value
        - Atom range
      * - Default
        - None
   
   Assign the atoms that are fixed during geometry optimization. For example:

   .. code-block:: bash
      :linenos:

      opt
        fix_atom 2 5-9 23 26
      end   

   The atoms 2,5,6,7,8,9,23,26 will be fixed during geometry optimization.

.. option:: fix_bond

   .. list-table::
      :stub-columns: 1
      :widths: 5 20
   
      * - Value
        - 2 integers
      * - Default
        - None
   
   Assign the bond that are fixed during geometry optimization. For example:

   .. code-block:: bash
      :linenos:

      opt
        fix_bond 1 4
        fix_bond 2 6
      end   

   The bonds (1,4) and (2,6) will be fixed during geometry optimization.

.. option:: fix_angle

   .. list-table::
      :stub-columns: 1
      :widths: 5 20
   
      * - Value
        - 3 integers
      * - Default
        - None
   
   Assign the angle that are fixed during geometry optimization. For example:

   .. code-block:: bash
      :linenos:

      opt
        fix_angle 1 4 5
        fix_angle 2 6 7
      end   

   The angles (1, 4, 5) and (2, 6, 7) will be fixed during geometry optimization.   

.. option:: fix_torsion

   .. list-table::
      :stub-columns: 1
      :widths: 5 20
   
      * - Value
        - 4 integers
      * - Default
        - None
   
   Assign the torsion that are fixed during geometry optimization. For example:

   .. code-block:: bash
      :linenos:

      opt
        fix_torsion 1 4 5 9
        fix_torsion 2 6 7 12
      end   

   The torsions (1, 4, 5, 9) and (2, 6, 7, 12) will be fixed during geometry optimization.