Name
CGDIIS — Use DIIS during conjugate-gradient steps.
Description
PSOLVE=CGDMS and
PSOLVE=QNDMS solve for the density matrix
using a congugate gradient (CG) procedure. To help improve convergence during CG, direct inversion of the iterative
subspace (DIIS) is used to extrapolate the density matrix at each step. (This is distinct from
SCFDIIS, which is applied at the SCF level.)
This procedure requires the storage of a set of density matrices and their corresponding error matrices.
Increasing the number of matrices used can potentially improve performance but will also increase the
memory used. By default, CG DIIS is turned on with n=10, which has been found to be
a good compromise. (If the number of CG iterations is smaller than this value, the DIIS storage is reduced accordingly.)
Setting n = 2 or less, will turn off CG DIIS. QNDMS, unlike CGDMS, requires CG DIIS and so
will not allow this value to be set below 4.
