Ceilidh ... Re^5: How to speed up the HESSIAN calculations

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Re^5: How to speed up the HESSIAN calculations

Dear Siddheshwar,
hssend=.t. is applicable for RUNTYP=OPTIMIZE or SADPOINT and means just evaluate (not compute!) hessian in the end of optimization run provided it's successful. This hessian is not exact, especially if your stationary point is far from optimization start, in some cases there can even be some imaginary frequencies that disappear when you recompute hessian. So, to make sure that you've reached stationary point of needed order, just recompute hessian (RUNTYP=HESSIAN with NVIB=2 to make sure) than put it into input file with HESS=READ option in $STATPT group and do optimization again (probably with less OPTTOL value). And you, of course, may add HSSEND=.t. key as it won't take much time for hessian evaluation. If stationary point won't be too far from starting point of this optimization, you may trust this hessian.
Another way (e.g. if you're searching for a minimum and predicting possible structure) is to start optimization with HESS=CALC (and as it's written above).
If you're searching for TS, its not as simple. In many cases it's useless to start TS search without RUNTYP=HESS results' analysis.

On Wed Jan 9 '13 11:39am, Siddheshwar Chopra wrote
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>Dear Pasha,
>Yes true Sir. If I am not wrong, both the runtyp=hessian and hessend=.t. mean the same???

>Regards,

>On Tue Jan 8 '13 8:00pm, Solntsev Pasha wrote
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>>Dear Siddheshwar.

>>One more thing. You don't need specify runtyp=hessian and hessend=.t. simultaneously. Use only runtyp=hessian for hessian matrix calculation.

Thu Jan 10 '13 12:20pm

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