[Pw_forum] About ecutwfc and ecutrho again

Nicola Marzari marzari at MIT.EDU
Fri Dec 21 05:52:56 CET 2007

Roughly speaking, the higher ecutwfc among the elements

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.


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  

Prof Nicola Marzari   Department of Materials Science and Engineering
13-5066   MIT   77 Massachusetts Avenue   Cambridge MA 02139-4307 USA
tel 617.4522758 fax 2586534 marzari at mit.edu http://quasiamore.mit.edu

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