forte2.orbitals.avas
====================

.. py:module:: forte2.orbitals.avas




Module Contents
---------------

.. py:class:: AVAS

   Bases: :py:obj:`forte2.base_classes.mixins.MOsMixin`, :py:obj:`forte2.base_classes.mixins.SystemMixin`, :py:obj:`forte2.base_classes.mixins.MOSpaceMixin`


   
   Atomic valence active space (AVAS) method for selecting active orbitals for multi-reference calculations.


   :Parameters:

       **subspace** : list
           The subspace of orbitals to be considered for AVAS selection.

       **subspace_pi_planes** : list, optional
           A list of planes defined by atoms in the molecule, used to determine π orbitals.

       **selection_method** : str, optional, default="cumulative"
           The method for selecting active orbitals. Options are "cumulative", "cutoff", "separate", and "total".
           - "cumulative": Selects orbitals based on cumulative eigenvalues of the overlap matrix. Must define `sigma`.
           - "cutoff": Selects orbitals based on a cutoff value for eigenvalues of the overlap matrix. Must define `cutoff`.
           - "separate": Selects occupied and virtual orbitals separately. Must define `num_active_docc` and `num_active_uocc`.
           - "total": Selects a total number of active orbitals. Must define `num_active`.

       **diagonalize** : bool, optional, default=True
           Whether to diagonalize the occupied and virtual space overlap matrices.

       **sigma** : float, optional, default=0.98
           Cumulative cutoff for the eigenvalues of the overlap matrix, controlling the size of the active space.

       **cutoff** : float, optional, default=1.0
           Cutoff for the eigenvalues of the overlap matrix; eigenvalues greater than this value are considered active.

       **evals_threshold** : float, optional, default=1.0e-6
           Threshold below which an eigenvalue of the projected overlap is considered zero.

       **num_active_docc** : int, optional, default=0
           Number of active doubly occupied orbitals. This is on top of any singly occupied orbitals if an ROHF reference is used.

       **num_active_uocc** : int, optional, default=0
           Number of active unoccupied orbitals.

       **num_active** : int, optional, default=0
           Total number of active orbitals. Again, this is on top of any singly occupied orbitals if an ROHF reference is used.











   .. rubric:: Notes

   The allow subspace specification is a list of strings, non-exhaustive examples::

   - ["C"]              # all carbon atoms
   - ["C","N"]          # all carbon and nitrogen atoms
   - ["C1"]             # carbon atom #1
   - ["C1-3"]           # carbon atoms #1, #2, #3
   - ["C(2p)"]          # the 2p subset of all carbon atoms
   - ["C(1s)","C(2s)"]  # the 1s/2s subsets of all carbon atoms
   - ["C1-3(2s)"]       # the 2s subsets of carbon atoms #1, #2, #3
   - ["Ce(4fzx2-zy2)"]  # the 4f zxx-zyy orbital of all Ce atoms

   See `J. Chem. Theory Comput. 2017, 13, 4063-4078 <https://doi.org/10.1021/acs.jctc.7b00128>`_ for details on the AVAS method.



   ..
       !! processed by numpydoc !!

   .. py:attribute:: subspace
      :type:  list


   .. py:attribute:: subspace_pi_planes
      :type:  list
      :value: None



   .. py:attribute:: selection_method
      :type:  str
      :value: 'cumulative'



   .. py:attribute:: diagonalize
      :type:  bool
      :value: True



   .. py:attribute:: sigma
      :type:  float
      :value: 0.98



   .. py:attribute:: cutoff
      :type:  float
      :value: 1.0



   .. py:attribute:: evals_threshold
      :type:  float
      :value: 1e-06



   .. py:attribute:: num_active
      :type:  int
      :value: 0



   .. py:attribute:: num_active_docc
      :type:  int
      :value: 0



   .. py:attribute:: num_active_uocc
      :type:  int
      :value: 0



   .. py:attribute:: executed
      :type:  bool
      :value: False



   .. py:method:: run()