[Pw_forum] About ecutwfc and ecutrho again

[Nicola Marzari]

Roughly speaking, the higher ecutwfc among the elements
considered.

Are these ultrasoft or norm conserving ? If the latter,
ecutrho could have been safely kept to 240 Ry.

If the former, my rule of thumb is that rarely a cutoff
greater than 30 Ry is needed, unless subtle magnetic/spin
propertes are sought. Thi sis to say that absolute convergence of
the energy is not the most useful criterion - often one looks
at lattice parameter, bulk modulus, or phonon frequencies as
good indicators of convergence.

				nicola

Huiqun Zhou wrote:
> Dear PWscfers,
> 
> I'm creating and testing pseudopotentials for severval
> elements myself. I plotted the E-ecutwfc graphs for 
> each element, in which the ecutwfc was ranging from 20
> to 60 with increament of 5 Ry and ecutrho was set to 600.
> If take 1 mRy as convergence criterion, I find that the
> total energy for some elements will be convergent at
> ecutwfc = 35 Ry while some are around ecutwfc = 55 Ry.
> 
> If the material I'm interested in is comprised from elements
> with both lower and higher ecutwfc, what ecutwfc should I
> set for the material, the higher one, the higher one plus
> alpha, or a compromise between the lower and higher?
> 
> Thnaks!
> 
> 
> Dr. Huiqun Zhou
> @Earth Sciences, Nanjing University, China  


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