Frequency calculation of very large systems

jquertin

Hi all,
I'm working on large unit cells (300+ atoms).
With the computational resources that I have, I cannot run the frequency calculation "reasonably".
Does anyone knows if there would be a trick such as running subsequent calculation using restarts and fragments of increasing size? Or even better, having multiple calculations with different parts of the cell and bringing them all together for the thermodynamics?
Thanks in advance,
Jean

aerba

Hi,

I think that the best way to proceed in this case would be to restart the calculation one or more times. To do this, you just have to make sure that the scratch folder is not deleted when the calculation stops. Basically, you would run a first job with:

FREQCALC
END

Then, after the first calculation stops (maybe because you reached a wall clock time limit) you would run a second job restarting from the first as:

FREQCALC
RESTART
END

In order to make this restart work, you need a few files from the previous job to be placed in the scratch folder of the new job: FREQINFO.DAT, fort.13 and fort.9 (to be renamed fort.20 in the new folder).

If needed, you can repeat this restart process multiple times until completion of the frequency calculation.

Hope this helps,