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Re: Problem in Geometry optimization

Thomas Pijper

Dear Arshad,

Though your initial geometry isn't ideal (I assume the geometry was determined using X-ray -- solid state geometries are usually quite different from gas phase geometries), it optimizes nicely, though a bit slow. The problem is that your optimization convergence criterion is too tight. The default value for OPTTOL is 1E-4, whereas you've requested 1E-7. I'd say that 2E-5 to 2E-6 is enough for most purposes.

If you really need the 1E-7 criterion accuracy, you will have to increase the accuracy of various parameters of the calculation. Some you have already provided (INTTYP=HONDO for example) but a few more are important for 1E-7 accuracy. Most importantly, I would change ICUT from 10 to at least 12. There are also a few more keyword in the $DFT group that could be set tighter (such as CUTOFF).

Some additional comments:
- NCONV is specified twice. I expect that NCONV=7 in your case would be fine.
- You have requested D5=.T. though the basis set you are using was designed for use with D5=.F.

Hope this helps.

Kind regards,

On Fri Sep 20 '13 5:42pm, Arshad Mehmood wrote
>Respected members,
>I am trying to optimize the geometry of Aspirin molecule. Though I am using a cif file (attached) for atomic coordinates, but it is not being optimized. Can any body solve my problem? Input and some part of output file is attached herewith.
>I am waiting your response.


[ This message was edited on Sun Sep 22 '13 at 12:50pm by the author ]

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