41 lines
1.8 KiB
ReStructuredText
41 lines
1.8 KiB
ReStructuredText
=========
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scf_utils
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=========
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The scf_utils module is an abstract module which contains the basics to perform *Restricted* SCF calculations (the
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spatial part of the |MOs| is common for alpha and beta spinorbitals) based on a single-determinant wave function.
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This module does not produce any executable *and must not do*, but instead it contains everything one needs to perform an orbital optimization based on an Fock matrix.
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The ``scf_utils`` module is meant to be included in the :file:`NEED` of the various single determinant SCF procedures, such as ``hartree_fock`` or ``kohn_sham``, where a specific definition of the Fock matrix is given (see :file:`hartree_fock fock_matrix_hf.irp.f` for an example).
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All SCF programs perform the following actions:
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#. Compute/Read all the one- and two-electron integrals, and store them in memory
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#. Check in the |EZFIO| database if there is a set of |MOs|. If there is, it
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will read them as initial guess. Otherwise, it will create a guess.
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#. Perform the |SCF| iterations based on the definition of the Fock matrix
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The main keywords/options are:
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* :option:`scf_utils thresh_scf`
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* :option:`scf_utils level_shift`
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At each iteration, the |MOs| are saved in the |EZFIO| database. Hence, if the calculation
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crashes for any unexpected reason, the calculation can be restarted by running again
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the |SCF| with the same |EZFIO| database.
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The `DIIS`_ algorithm is implemented, as well as the `level-shifting`_ method.
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If the |SCF| does not converge, try again with a higher value of :option:`level_shift`.
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To start a calculation from scratch, the simplest way is to remove the
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``mo_basis`` directory from the |EZFIO| database, and run the |SCF| again.
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.. _DIIS: https://en.wikipedia.org/w/index.php?title=DIIS
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.. _level-shifting: https://doi.org/10.1002/qua.560070407
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