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qp2/docs/source/modules/kohn_sham.rst

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.. _module_kohn_sham:
.. program:: kohn_sham
.. default-role:: option
=========
kohn_sham
=========
The Kohn-Sham module performs *Restricted* Kohn-Sham calculations (the
spatial part of the |MOs| is common for alpha and beta spinorbitals).
The Kohn-Sham in an SCF and therefore is based on the ``scf_utils`` structure.
It performs the following actions:
#. Compute/Read all the one- and two-electron integrals, and store them in memory
#. Check in the |EZFIO| database if there is a set of |MOs|. If there is, it
will read them as initial guess. Otherwise, it will create a guess.
#. Perform the |SCF| iterations
The definition of the Fock matrix is in :file:`kohn_sham fock_matrix_ks.irp.f`
For the keywords related to the |SCF| procedure, see the ``scf_utils`` directory where you will find all options.
The main are:
#. :option:`scf_utils thresh_scf`
#. :option:`scf_utils level_shift`
At each iteration, the |MOs| are saved in the |EZFIO| database. Hence, if the calculation
crashes for any unexpected reason, the calculation can be restarted by running again
the |SCF| with the same |EZFIO| database.
The `DIIS`_ algorithm is implemented, as well as the `level-shifting`_ method.
If the |SCF| does not converge, try again with a higher value of :option:`level_shift`.
To start a calculation from scratch, the simplest way is to remove the
``mo_basis`` directory from the |EZFIO| database, and run the |SCF| again.
.. _DIIS: https://en.wikipedia.org/w/index.php?title=DIIS
.. _level-shifting: https://doi.org/10.1002/qua.560070407
Programs
--------
* :ref:`ks_scf`
Providers
---------
.. c:var:: ks_energy
File : :file:`ks_enery.irp.f`
.. code:: fortran
double precision :: ks_energy
double precision :: two_e_energy
double precision :: one_e_energy
double precision :: fock_matrix_energy
double precision :: trace_potential_xc
Kohn-Sham energy containing the nuclear repulsion energy, and the various components of this quantity.
Needs:
.. hlist::
:columns: 3
* :c:data:`ao_num`
* :c:data:`ao_one_e_integrals`
* :c:data:`ao_potential_alpha_xc`
* :c:data:`ao_two_e_integral_alpha`
* :c:data:`e_correlation_dft`
* :c:data:`e_exchange_dft`
* :c:data:`fock_matrix_ao_alpha`
* :c:data:`nuclear_repulsion`
* :c:data:`scf_density_matrix_ao_alpha`
* :c:data:`scf_density_matrix_ao_beta`
Needed by:
.. hlist::
:columns: 3
* :c:data:`extra_e_contrib_density`
Subroutines / functions
-----------------------