SCFDIIS — Use DIIS to improve convergence of the SCF.
Direct inversion of the iterative subspace (DIIS) is used by default to improve SCF convergence when using
PSOLVE methods. (This is different from
CGDIIS which is used as part of a solver during an
individual SCF cycle.) At the beginning of each SCF cycle, DIIS is used to extrapolate the Fock matrix
which is then used in solving for the density marix. DIIS requires the storage of a set of
Fock matrices and their corresponding error matrices, which are used in the extrapolation process.
Increasing the number of matrices used can potentially improve performance but will also increase the
memory required to store them. By default, SCF-DIIS is turned on with
which gives good results without being overly costly. This keyword can be used to adjust the number of
matrices stored and used within the DIIS proceedure. Setting
n = 2 or less,
will turn off SCF DIIS.
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