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24.7 The DIIS directive


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

First iteration in which DIIS extrapolation may be performed (default=2).
Increment between DIIS iterations (default=1).
Maximum number of expansion vectors to be used (default=6).
DIIS extrapolation type. itydis=1 (default): residual is minimized. itydis=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. 2018-07-21