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39 lines
1.3 KiB
ReStructuredText
39 lines
1.3 KiB
ReStructuredText
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====
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cisd
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====
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This module contains a CI of single and double excitations.
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The user point of view
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----------------------
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The :command:`cisd` program performs the CI of the ROHF-like + all single and double excitations on top of it.
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This program can be very useful to :
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* **Ground state calculations**: generate a guess for the ground state wave function if one is not sure that the :c:func:`scf` program gave the lowest SCF solution. In combination with :c:func:`save_natorb` it can produce new |MOs| in order to reperform an :c:func:`scf` optimization.
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* **Excited states calculations**: generate guess for all the :option:`determinants n_states` wave functions, that will be used by the :c:func:`fci` program.
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The main keywords/options to be used are:
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* :option:`determinants n_states` : number of states to consider for the |cisd| calculation
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* :option:`determinants s2_eig` : force all states to have the desired value of :math:`S^2`
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* :option:`determinants expected_s2` : desired value of :math:`S^2`
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The programmer point of view
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----------------------------
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This module have been built by setting the following rules:
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* The only generator determinant is the Hartree-Fock (single-reference method)
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* All generated determinants are included in the wave function (no perturbative
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selection)
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These rules are set in the ``H_apply.irp.f`` file.
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