=== 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.