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
<[email protected] <mailto:[email protected]>> 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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