mirror of
https://github.com/LCPQ/quantum_package
synced 2024-06-02 11:25:26 +02:00
179 lines
4.5 KiB
ReStructuredText
179 lines
4.5 KiB
ReStructuredText
.. _fci:
|
|
|
|
.. program:: fci
|
|
|
|
.. default-role:: option
|
|
|
|
===
|
|
fci
|
|
===
|
|
|
|
|
|
|CIPSI| algorithm in the full configuration interaction space.
|
|
|
|
|
|
The user point of view
|
|
----------------------
|
|
|
|
* :c:func:`fci` performs |CIPSI| calculations using a stochastic scheme for both the selection and the |PT2| contribution,
|
|
* :c:func:`pt2` computes the |PT2| contribution using the wave function stored in the |EZFIO|
|
|
database.
|
|
|
|
|
|
The main keywords/options for this module are:
|
|
|
|
* :option:`determinants n_det_max` : maximum number of Slater determinants in the CIPSI wave function. The :command:`fci` program will stop when the size of the CIPSI wave function will exceed :option:`determinants n_det_max`.
|
|
|
|
* :option:`perturbation pt2_max` : absolute value of the |PT2| to stop the CIPSI calculation. Once the |PT2| :math:`<` :option:`perturbation pt2_max`, the CIPSI calculation stops.
|
|
|
|
* :option:`determinants n_states` : number of states to consider in the CIPSI calculation.
|
|
|
|
* :option:`determinants read_wf` : if False, starts with a ROHF-like determinant, if True, starts with the current wave function(s) stored in the |EZFIO| folder.
|
|
|
|
.. note::
|
|
For a multi-state calculation, it is recommended to start with :c:func:`cis` or :c:func:`cisd`
|
|
wave functions as a guess.
|
|
|
|
* :option:`determinants s2_eig` : if True, systematically add all the determinants needed to have a pure value of :math:`S^2`. Also, if True, it tracks only the states having the good :option:`determinants expected_s2`.
|
|
|
|
.. note::
|
|
For a multi-state calculation, it is recommended to start with :c:func:`cis` or :c:func:`cisd`
|
|
wave functions as a guess.
|
|
|
|
* :option:`determinants expected_s2` : expected value of :math:`S^2` for the desired spin multiplicity.
|
|
|
|
|
|
|
|
The programmer point of view
|
|
----------------------------
|
|
|
|
This module have been created with the :ref:`cipsi` module.
|
|
|
|
.. seealso::
|
|
|
|
The documentation of the :ref:`cipsi` module.
|
|
|
|
|
|
|
|
|
|
|
|
EZFIO parameters
|
|
----------------
|
|
|
|
.. option:: energy
|
|
|
|
Calculated Selected |FCI| energy
|
|
|
|
|
|
.. option:: energy_pt2
|
|
|
|
Calculated |FCI| energy + |PT2|
|
|
|
|
|
|
|
|
Providers
|
|
---------
|
|
|
|
|
|
.. c:var:: nthreads_pt2
|
|
|
|
.. code:: text
|
|
|
|
integer :: nthreads_pt2
|
|
|
|
File: :file:`environment.irp.f`
|
|
|
|
Number of threads for Davidson
|
|
|
|
|
|
|
|
|
|
Subroutines / functions
|
|
-----------------------
|
|
|
|
|
|
|
|
.. c:function:: fci
|
|
|
|
.. code:: text
|
|
|
|
subroutine fci
|
|
|
|
File: :file:`fci.irp.f`
|
|
|
|
Selected Full Configuration Interaction with stochastic selection and PT2 .
|
|
|
|
This program performs a CIPSI-like selected CI using a stochastic scheme for both
|
|
|
|
the selection of the important Slater determinants and the computation of the PT2 correction.
|
|
|
|
This CIPSI-like algorithm will be performed for the "n_states" lowest states of the variational space (see :option:`determinants n_det_max`)
|
|
|
|
The fci program will stop when reaching at least one the two following conditions:
|
|
|
|
* number of Slater determinant > "n_det_max" (see :option:`determinants n_det_max`)
|
|
|
|
* |PT2| < "pt2_max" (see :option:`perturbation pt2_max`)
|
|
|
|
|
|
|
|
The following other options can be of interest:
|
|
|
|
If "read_wf" = False, it starts with a ROHF-like Slater determinant as a guess wave function.
|
|
|
|
If "read_wf" = True , it starts with the wave function(s) stored in the EZFIO folder as guess wave function(s).
|
|
|
|
(see :option:`determinants read_wf`)
|
|
|
|
If "s2_eig" = True, it will systematically add all necessary Slater determinants in order
|
|
|
|
to have a pure spin wave function with an :math:`S^2` value corresponding to "expected_s2".
|
|
|
|
(see :option:`determinants s2_eig` and :option:`determinants expected_s2`)
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
For excited states calculations, it is recommended to start with a :c:func:`cis` or :c:func:`cisd` guess wave functions
|
|
|
|
for the "n_states", and to set "s2_eig" = True.
|
|
|
|
|
|
|
|
|
|
|
|
.. c:function:: pt2
|
|
|
|
.. code:: text
|
|
|
|
subroutine pt2
|
|
|
|
File: :file:`pt2.irp.f`
|
|
|
|
Second order perturbative correction to the wave function contained in the EZFIO directory.
|
|
|
|
This programs runs the stochastic PT2 correction on all "n_states" wave function stored in the EZFIO folder (see :option:`determinant n_states`).
|
|
|
|
The option for the PT2 correction are the "pt2_relative_error" which is the relative stochastic
|
|
|
|
error on the PT2 to reach before stopping the stochastic sampling. (see :option:`perturbation pt2_relative_error`)
|
|
|
|
|
|
|
|
|
|
|
|
.. c:function:: save_energy
|
|
|
|
.. code:: text
|
|
|
|
subroutine save_energy(E,pt2)
|
|
|
|
File: :file:`save_energy.irp.f`
|
|
|
|
Saves the energy in |EZFIO|.
|
|
|
|
|