24.5 The DIIS directive

DIIS,itedis,incdis,maxdis,itydis;

This directive allows to modify the DIIS parameters for CCSD, QCISD, or BCCD calculations.

itedis:

First iteration in which DIIS extrapolation may be performed (default=4).

incdis:

Increment between DIIS iterations (default=1).

maxdis:

Maximum number of expansion vectors to be used (default=6).

itydis:

DIIS extrapolation type. itedis=1 (default): residual is minimized. itedis=2: $\Delta T$ is minimized.

In addition, there is a threshold THRDIS which may be modified with the THRESH directive. DIIS extrapolation is only done if the variance is smaller than THRDIS.