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