[gpaw-users] Convergence issue with mBEEF

[Jess Wellendorff]

On 11/26/2014 03:53 PM, Jens Jørgen Mortensen wrote:
> On 11/25/2014 10:44 PM, Jess Wellendorff wrote:
>> Marcin: The mBEEf functional was fitted on PBEsol electron densities 
>> obtained using rather tight SCF criteria. I think something else must 
>> be the root cause of this issue. Perhaps GPAW does not supply LibXC 
>> with sufficiently accurate kinetic energy densities?
>>
>> Monish: Honestly, I believe the only solution to your problem is to 
>> lower the SCF convergence criteria, perhaps even completely eliminate 
>> them for the eigenstates and rely only on density and energy 
>> criteria. I have successfully used this approach. It is not pretty, 
>> but it works :)
>>
>> If you take a look at the mBEEF test script (gpaw/test/mbeef.py), the 
>> SCF criteria for very quick molecular calculatios are set to 
>> {'eigenstates':1.e+2, 'density':1.e-2, 'energy':1.e-4}. These are 
>> bullet-proof settings for a simple test. In general, the density and 
>> energy criteria can probably be tightened more. Also, I would expect 
>> the eigenstate issue to be much less pronounced in bulk calculations.
>
> What is it that makes mBEEF so special?  I'm struggling with a test 
> calculation for a nitrogen atom (not mBEEF, but mBEEF-vdW) and I can 
> also not converge the eigenstates.  Strange thing is that TPSS works 
> fine.
>
> It helped a bit to use eigensolver='rmm-diis'.
>
> Jens Jørgen
You're absolutely right. I will have to look into this.
- Jess
>
>>
>> Hope this helps.
>> Best,
>> Jess
>>
>> On 11/25/2014 06:53 PM, Marcin Dulak wrote:
>>> On 11/25/2014 04:37 PM, Wellendorff, Jess wrote:
>>>> Hi Monish, in my experience, the eigenstates can be hard to 
>>>> converge with metagga. Is this your problem?
>>> i remember even with the older BEEF-vdW molecules are hard to converge.
>>> Maybe this is due to loose SCF thresholds used when fitting the 
>>> functional (was it the case also for mBEEF?),
>>> so the resulting functional by design is not reaching a tight 
>>> convergence.
>>>
>>> Best regards,
>>>
>>> Marcin
>>>>
>>>> Best,
>>>> Jess
>>>>
>>>>
>>>>> On Nov 25, 2014, at 14:48, mohnish pandey <mohnish.iitk at gmail.com> 
>>>>> wrote:
>>>>>
>>>>> Dear all,
>>>>>
>>>>> I am trying to do some test calculations with mBEEF functional for 
>>>>> some solids like ZnO. But I am facing difficulty in converging the 
>>>>> calculations. I tried tweaking mixing, Fermi temperature etc, but 
>>>>> it didn't help. Would really appreciate if somebody helps me out 
>>>>> with the issue. Thanks a lot in advance.
>>>>>
>>>>> -- 
>>>>> Regards,
>>>>> Mohnish,
>>>>> -----------------------------------------------------------------
>>>>> Mohnish Pandey,
>>>>> PhD Student,
>>>>> Center for Atomic-scale Materials Design,
>>>>> Department of Physics,
>>>>> Technical University of Denmark
>>>>> -----------------------------------------------------------------
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>>
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