I'm sorry for some delay with my reply.
The present implementation of gdiis in Firefly works as follows.
The very initial steps are performed using QA method just to gather
statistics. The number of QA steps to use is controlled by the NSKIP
keyword in the $statpt group. The default is nskip=2.
After performing initial QA steps, algorithm switches to gdiis.
While working in the gdiis mode, it is still possible for algorithm
to select pure NR step if it seems to be more efficient at a given
geometry update step. This fallback to NR steps can be disabled by
setting MIXED keyword of $statpt group to .false.
Finally, if gdiis is invoked for TS searche, it executes QA procedure.
Hope this helps.
All the best,
On Thu Dec 19 '13 5:20pm, Slawomir Janicki wrote
>How can I delay switching from GDIIS to NR method in geometry optimization?
>When NR kicks in a large step causes SCF convergence to fail, presumably because of a bad guess. I tried to decrease DXMAX to 0.001, but there seems to be no effect on when NR starts.
>Is there a better way to delay or prevent switching to NR? Alternatively, is there a way to reduce the NR step size?
>Below is an example of the step when NR starts:
MAXIMUM GRADIENT = 0.0462724 RMS GRADIENT = 0.0142135 FORCE CONSTANT MATRIX NOT UPDATED --- TAKING FIRST STEP MIN SEARCH, CORRECT HESSIAN, TRYING PURE NR STEP NR STEP HAS LENGTH = 92.651197 TRIM/QA LAMBDA FOR NON-TS MODES = -84.40598785 TRIM/QA STEP HAS LENGTH = 0.001000 RADIUS OF STEP TAKEN= 0.00100 CURRENT TRUST RADIUS= 0.00100 TRANSFORMING DISPLACEMENT FROM INTERNALS TO CARTESIANS THE ROOT MEAN SQUARE ERROR IN ITERATION 1 IS 0.00000001 THE ROOT MEAN SQUARE ERROR IN ITERATION 2 IS 0.00000000 MAX PRIMITIVE INTERNAL COORDINATE DEVIATION IS 0.00000000 INTERNAL COORDINATES SELF-INCONSISTENCY IS 0.00000303