[CP2K:2039] Re: optimisation problem of F compound

[Fawzi Mohamed]

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
>
>