[Pw_forum] [Fwd: Discrepancy on plotband.x output]

[Giovanni Cantele]

Dear Youssef,

some remarks:

i) the “total” band structure is, as far as I know, meaningless. While for the DOS you can sum dos-up and dos-down of
a spin polarized calculation, to get the total DOS, for the band structure you can just put, in the same plot, the up and down
band structures. As such, when you run bands.x without setting the variable spin_component, it automatically takes the default
value, which is 1. Indeed, what you call the “total” band structure, is nothing else than the spin-up band structure

ii) from the above remark, your total DOS could actually correctly match the DOS, in that, for example, the spin up band structure
has a gap (very roughly estimations looking at your plots) from about -2 eV to about 3 eV, whereas the spin down band structure a gap from about
-3 eV to about -0.5 eV and from about 0.2-0.3 eV to about 2.5 eV, which seems to agree with the DOS plot

iii) if you want to plot the total (spin up and/or down) DOS of your system, the steps you follow are wrong. dos.x shouldn’t be run after bands.x,
because this would give you JUST the contribution to the total DOS from the bands at the selected k-points in you band structure path. BEFORE
dos.x you should run another nscf calculation, with a k-point grid much finer that that needed in scf (e.g. 4x4x4 might be enough to ensure convergence
of your ground-state density, but a 16x16x16 or 32x32x32 might be needed to give a meaningful plot of your DOS). Typically, if you plot the DOS
after an nscf calculation with a rough sampling of the Brillouin zone, you might end up with a plot where you have lot of (“atomic-like”) spikes, which
are actually unphysical and give you the indication of a badly performed integral over the Brillouin zone.

Giovanni

> On 16 Feb 2015, at 08:49, Youssef <aharbil at gmail.com> wrote:
> 
> Dear quantum espresso community,
> 
> I have attached 4 files according to my target compound :
> 
> dos.jpg   ==> describe the total density of states 
>  x.jpg   ==> describe the band structure (Total ) 
> up.jpg   ==> describe the total band structure (spin up) 
> up.jpg   ==> describe the total band structure (spin down) 
> 
> all the calculation have been performed from the same input files (same
> k path ) in this order:
> 
> pw.x ==> scf
> pw.x ==> nscf ( denser grid = 1.5 x scf grid)
> pw.x ==> bands { special path :  
> 
> K_POINTS tpiba_b
>  6
>   W 25
>   L 25
>  gG 25
>   X 25
>   W 25
>   K 25
> }
> 
> bands.x  ==> without spin_component   ==>plotband.x
> bands.x  ==> with spin_component = 1  ==>plotband.x
> bands.x  ==> with spin_component = 2 ==>plotband.x
> dos.x
> projwfc.x
> 
> 
> and as you can realize:
> 
> The total band structure disagree with the total dos describing the
> metallic behavior , OK, let's say that I missed the K path where the
> metallicity behavior came from, but why isn't the case for spin down
> band structure that in contract agree very well with total dos) 
> 
> 
> Youssef Aharbil,
> Laboratory of Physics and Chemistry of Materials
> Faculty of sciences Ben msik, Casablanca
> Morocco
> 
> <dw.jpg><up.jpg><x.jpg><dos.jpg>_______________________________________________
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-- 

Giovanni Cantele, PhD
CNR-SPIN
c/o Dipartimento di Fisica
Universita' di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
e-mail: giovanni.cantele at spin.cnr.it
Phone: +39 081 676910
Skype contact: giocan74

ResearcherID: http://www.researcherid.com/rid/A-1951-2009
Web page: http://people.na.infn.it/~cantele