[CP2K:2043] Re: optimisation problem of F compound

[Fawzi Mohamed]

Hi Jörg,

On 24-apr-09, at 01:39, Jörg Saßmannshausen wrote:

> Dear Axel,
>
> yep, there are plenty in the BASIS_MOLOPT.
> However, I was not sure if they are suitable for my problem, hence I  
> did not
> use them. However, I will give it a try.

I don't think that the problem with imaginary frequency is due to the  
basis set, that said the MOLOPT basis set is normally a good choice :)

I saw another thing you use EPS_SCF 1.0E-8, in this case you should  
increase also EPS_DEFAULT, so that the integrals are more accurate,  
otherwise you might have problems converging. In general one should  
have EPS_DEFAULT ~ EPS_SCF^2, but due to the numerical accuracy  
probably it does not make any sense to go higher than 1.0E-15.

ciao

Fawzi

>
>
> Thanks for your help!
>
> Jörg
>
>
> On Donnerstag 23 April 2009 Axel wrote:
>> On Apr 23, 5:25 pm, Jörg Saßmannshausen
>>
>> <jorg.sassm... at strath.ac.uk> wrote:
>>> Dear Fawzi,
>>>
>>> thanks for shedding some light into it (which is easy if it is  
>>> sunny :-)
>>> :-)
>>>
>>> I am playing around with that problem now for some time.  
>>> Previously I
>>> used BLYP (on a larger system but with the same compound in it)  
>>> and I got
>>> a imaginary frequency which was again movement of the F atom.
>>> So I cut down the system and followed Axel's suggestion to use  
>>> PBE. As I
>>> could not find a PBE optimised basis set for F, I tried the two I
>>> mentioned. With both I had the imaginary frequencies.
>>
>> there are plenty of basis set variations for F in BASIS_MOLOPT.
>>
>> axel.
>>
>>> I agree with the forces, I think that was what my gutt tried to  
>>> tell me.
>>> I got the feeling the cluster will be very busy tonight ;-)
>>>
>>> Greetings to Berlin and thanks!
>>>
>>> Jörg
>>>
>>> On Donnerstag 23 April 2009 Fawzi Mohamed wrote:
>>>> On 23-apr-09, at 22:35, Jörg Saßmannshausen wrote:
>>>>> Dear Fawzi,
>>>>>
>>>>> I actually did:
>>>>>
>>>>> cutoff energy
>>>>> 400  -183.5957955549
>>>>> 450  -183.5944280905
>>>>> 500  -183.5937679158
>>>>> 550  -183.5935371009
>>>>> 600  -183.5938000945
>>>>>
>>>>> one of the things I learned from Rachel at the workshop :-)
>>>>>
>>>>> For me it looked like that 500 seems to be ok, so I decided to go
>>>>> for that
>>>>> value.
>>>>> However, these values were for the DZVP-ALLELECTRON basis set. I  
>>>>> did
>>>>> not run a
>>>>> test for the aug-DZVP-GTH, simply assuming as I did not change the
>>>>> potential
>>>>> only the basis set the difference would be not that big?
>>>>
>>>> normally it is a good assumption to assume that the basis set  
>>>> does not
>>>> influence much the cutoff, but switching from GAPW (allelectron) to
>>>> GPW does change things, and a lot, gapw does not put the whole  
>>>> density
>>>> on the grid, so for it the cutoff is not critical.
>>>>
>>>>> Or was that a wrong
>>>>> assumption? What cutoff would you recommend?
>>>>
>>>> I haven't calculated with F, but from the high exponent in the  
>>>> basis
>>>> (10.7079832847), and also for p functions yo might need more I  
>>>> would
>>>> try 800.
>>>> Think that you need accurate forces, on *everything* and if you  
>>>> have
>>>> just one F looking just at the total energy might be misleading, if
>>>> you want to be sure do some steps of MD with HF or something like
>>>> that, and look at the energy conservation...
>>>>
>>>>> Thanks for the prompt reply!
>>>>
>>>> you are welcome.
>>>>
>>>>> All the best from a wet Glasgow!
>>>>
>>>> and greetings from sunny Berlin :)
>>>>
>>>> Fawzi
>>>>
>>>>> Jörg
>>>>>
>>>>> On Donnerstag 23 April 2009 Fawzi Mohamed wrote:
>>>>>> I would say that the cutoff of 500 might be too small for the F
>>>>>> element. Have you tested the cutoff needed for it?
>>>>>>
>>>>>> Fawzi
>>>>>>
>>>>>> On 23-apr-09, at 18:12, Jörg Saßmannshausen wrote:
>>>>>>> Dear all,
>>>>>>>
>>>>>>> I am struggling to optimise a molecular structure with a F  
>>>>>>> atom in
>>>>>>> it.
>>>>>>> Whereas I manage to get the optimisation converged, the  
>>>>>>> frequency
>>>>>>> calculation clearly indicates I am not at the local minimum.
>>>>>>> Replacing
>>>>>>> the F atom in the molecule with H (and leave everything else the
>>>>>>> same)
>>>>>>> results in a converged structure. I got the gutt-feeling that  
>>>>>>> the
>>>>>>> problem is the basis set / pseudopotential I am using for F.  
>>>>>>> Would
>>>>>>> somebody mind to give me a helping hand here?
>>>>>>>
>>>>>>> I have enclosed the following files:
>>>>>>> - mol file of the frequency calculation (so you see what I mean)
>>>>>>> - force_eval section
>>>>>>> - subsys section
>>>>>>> - fluor-geo.inp
>>>>>>> - fluor-freq.inp
>>>>>>>
>>>>>>> I had no problems with the molecule using a different program,  
>>>>>>> so
>>>>>>> I am
>>>>>>> quite confident about the structure. Note: it is a cation, I  
>>>>>>> left
>>>>>>> the
>>>>>>> anion out for computational reasons.
>>>>>>>
>>>>>>> Thanks for your help!
>>>>>>>
>>>>>>> Jörg
>>>
>>> --
>>> *************************************************************
>>> Jörg Saßmannshausen
>>> Research Fellow
>>> University of Strathclyde
>>> Department of Pure and Applied Chemistry
>>> 295 Cathedral St.
>>> Glasgow
>>> G1 1XL
>>>
>>> email: jorg.sassm... at strath.ac.uk
>>> web:http://sassy.formativ.net
>>>
>>> Please avoid sending me Word or PowerPoint attachments.
>>> Seehttp://www.gnu.org/philosophy/no-word-attachments.html
>>
>>
>
>
> -- 
> *************************************************************
> Jörg Saßmannshausen
> Research Fellow
> University of Strathclyde
> Department of Pure and Applied Chemistry
> 295 Cathedral St.
> Glasgow
> G1 1XL
>
> email: jorg.sassm... at strath.ac.uk
> web: http://sassy.formativ.net
>
> Please avoid sending me Word or PowerPoint attachments.
> See http://www.gnu.org/philosophy/no-word-attachments.html
>
>