.. _cis: 
 
.. program:: cis 
 
.. default-role:: option 
 
===
cis
===

This module contains a CIS program.

The user point of view
----------------------

The :command:`cis` program performs the CI of the ROHF-like + all single excitations on top of it.
This program can be very useful to :

* **Ground state calculations**: generate a guess for the ground state wave function if one is not sure that the :c:func:`scf` program gave the lowest SCF solution. In combination with :c:func:`save_natorb` it can produce new |MOs| in order to reperform an :c:func:`scf` optimization.

* **Excited states calculations**: generate guess for all the :option:`determinants n_states` wave functions, that will be used by the :c:func:`fci` program.


The main keywords/options to be used are:

* :option:`determinants n_states` : number of states to consider for the |CIS| calculation

* :option:`determinants s2_eig` : force all states to have the desired value of :math:`S^2`

* :option:`determinants expected_s2` : desired value of :math:`S^2`




The programmer point of view
----------------------------

This module have been built by setting the following rules:

* The only generator determinant is the Hartree-Fock (single-reference method)
* All generated singly excited determinants are included in the wave function (no perturbative
  selection)

These rules are set in the ``H_apply.irp.f`` file.


 
 
 
EZFIO parameters 
---------------- 
 
.. option:: energy
 
    Variational |CIS| energy
 
 
 
Programs 
-------- 
 
 * :ref:`cis` 
 
Subroutines / functions 
----------------------- 
 


.. c:function:: h_apply_cis

    .. code:: text

        subroutine H_apply_cis()

    File: :file:`h_apply.irp.f_shell_8`

    Calls H_apply on the |HF| determinant and selects all connected single and double excitations (of the same symmetry). Auto-generated by the ``generate_h_apply`` script.


 


.. c:function:: h_apply_cis_diexc

    .. code:: text

        subroutine H_apply_cis_diexc(key_in, key_prev, hole_1,particl_1, hole_2, particl_2, fock_diag_tmp, i_generator, iproc_in  )

    File: :file:`h_apply.irp.f_shell_8`

    


 


.. c:function:: h_apply_cis_diexcorg

    .. code:: text

        subroutine H_apply_cis_diexcOrg(key_in,key_mask,hole_1,particl_1,hole_2, particl_2, fock_diag_tmp, i_generator, iproc_in  )

    File: :file:`h_apply.irp.f_shell_8`

    Generate all double excitations of key_in using the bit masks of holes and particles. Assume N_int is already provided.


 


.. c:function:: h_apply_cis_diexcp

    .. code:: text

        subroutine H_apply_cis_diexcP(key_in, fs1, fh1, particl_1, fs2, fh2, particl_2, fock_diag_tmp, i_generator, iproc_in  )

    File: :file:`h_apply.irp.f_shell_8`

    


 


.. c:function:: h_apply_cis_monoexc

    .. code:: text

        subroutine H_apply_cis_monoexc(key_in, hole_1,particl_1,fock_diag_tmp,i_generator,iproc_in  )

    File: :file:`h_apply.irp.f_shell_8`

    Generate all single excitations of key_in using the bit masks of holes and particles. Assume N_int is already provided.