| 4:32:32 AM PDT - Tue, Jul 24th 2012 |
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Thanks Bert-
Actually these are numerical hessian calculations.
I have a 25-atom aquo ion vibrating in a fixed crystal (i.e. actlist is 1:25 in task dft optimize). The system has C2V symmetry (162 atoms total; 46 unique centers ). The aquo ion uses a large basis set, the surrounding crystal uses a smaller one.
The problem is that the "actlist" and "gen_hess" directives don't seem to allow restriction of the hessian evaluation to only the free core atoms in the system.
My plan is to just evaluate the whole hessian, and then extract the first 3x25 rows and columns for a frequency calculation (using a simple code that I wrote to do this).
Ideally, though, I would also like to avoid having to wait for all 46 unique atoms to be displaced.
It seems to me that once the symmetry-unique atoms in the aquo ion have been displaced, that it should, in principle, be possible to kill the job, pluck out the first 3x25 rows and columns of the hessian, and do the frequency calculation.
The problems are:
(1) I don't know how to extract the hessian out of the rtdb. It will not have been printed because the job would be killed prematurely.
(2) I don't know when the symmetry operations have been applied to the hessian; in other words, after the unique atoms in the core have all been displaced, are all of the first 3x25 columns and rows of the hessian intact, so that I could just read them directly out of the rtdb ? Or does the code not apply the symmetry until the end, after all unique atoms have been displaced?
I would think also that this task might come up often in QM-MM calculations- maybe there tools in these codes that might apply?
Thanks for all you help,
Jim R.
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