[QE-users] "Re2: Convergence Issues?"

[Nicola Marzari]

Dear Stefano, Lucas,

this is one of the few areas where I disagree with Stefano - I think we 
should use the free energy (forces and stresses are the total derivative 
of the free energy, not the internal energy), and that level-crossing 
instabilities are exceedinfly difficult to cure with iterative 
algorithms (my own opinions are here: 
http://theossrv1.epfl.ch/Main/ElectronicTemperature),


             nicola


On 25/01/2021 16:33, Stefano Baroni wrote:
> I beg to slight differ. It does not make much sense to assign a 
> “default value” to the Gaussian smearing, unless one makes sure that 
> the computations are well converged with respect to the number of k 
> points, for that specific value of the smearing. The rational 
> procedure to follow is: 1) start with whatever value of the smearing 
> one wishes, and make sure that the (internal, *not* “fake free”) 
> energy is well converged with respect to the number of k points. If 
> the number of k points is sufficient, it is likely that no nasty 
> oscillation would arise; 2) decrease the smearing and vary the number 
> of k points accordingly. HTH — Stefano B
>
>
> —
> Stefano Baroni -  SISSA, Trieste - http://stefano.baroni.me 
> <http://stefano.baroni.me>, stefanobaroni (skype)
>
> I do not mind if you think slowly, but I do object when you publish 
> more quickly than you think [W.E. Pauli to an unknown colleague, as 
> reported by N. Kemmer]
>
>> On 25 Jan 2021, at 15:08, Lucas Nicolás Lodeiro Moraga 
>> <lucas.lodeiro at ug.uchile.cl <mailto:lucas.lodeiro at ug.uchile.cl>> wrote:
>>
>> Hi,
>> It appears a metallic oscillation, where a couple or more states 
>> change their relative energy, and change their energetical order, 
>> then the occupation changes abruptly (non continuous). If this is the 
>> problem, it is better to increase the degauss value and/or change the 
>> smearing method.
>> Typically I use methfessel-paxton with 0.015 Ry for degauss, which 
>> mimics the VASP default values. When you get a converged system, you 
>> can try to decrease (slowly) the degauss.
>>
>> Regards - Lucas Lodeiro
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