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41 lines
1.9 KiB
ReStructuredText
41 lines
1.9 KiB
ReStructuredText
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============
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kohn_sham_rs
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============
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The Range-separated Kohn-Sham module performs *Restricted* Kohn-Sham calculations (the
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spatial part of the |MOs| is common for alpha and beta spinorbitals) where the coulomb interaction is partially treated using exact exchange.
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The splitting of the interaction between long- and short-range is determined by the range-separation parameter :option:`ao_two_e_erf_ints mu_erf`. The long-range part of the interaction is explicitly treated with exact exchange, and the short-range part of the interaction is treated with appropriate DFT functionals.
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The Range-separated Kohn-Sham in an SCF and therefore is based on the ``scf_utils`` structure.
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It performs 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
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The definition of the Fock matrix is in :file:`kohn_sham_rs fock_matrix_rs_ks.irp.f`
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For the keywords related to the |SCF| procedure, see the ``scf_utils`` directory where you will find all options.
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The main 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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