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51 lines
1.8 KiB
ReStructuredText
51 lines
1.8 KiB
ReStructuredText
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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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The user point of view
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----------------------
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* :c:func:`fci` performs |CIPSI| calculations using a stochastic scheme for both the selection and the |PT2| contribution,
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* :c:func:`pt2` computes the |PT2| contribution using the wave function stored in the |EZFIO|
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database.
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The main keywords/options for this module are:
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* :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`.
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* :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.
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* :option:`determinants n_states` : number of states to consider in the CIPSI calculation.
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* :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.
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.. note::
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For a multi-state calculation, it is recommended to start with :c:func:`cis` or :c:func:`cisd`
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wave functions as a guess.
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* :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`.
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.. note::
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For a multi-state calculation, it is recommended to start with :c:func:`cis` or :c:func:`cisd`
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wave functions as a guess.
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* :option:`determinants expected_s2` : expected value of :math:`S^2` for the desired spin multiplicity.
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The programmer point of view
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----------------------------
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This module have been created with the :ref:`cipsi` module.
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.. seealso::
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The documentation of the :ref:`cipsi` module.
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