[Pw_forum] how to add hydrostatic pressure on 2D mono-layer MoS2

[plgong]

Dear pw_user,
 I have try to set "press = 100kbar" on bulk MoS2, and it sucess; I can 
find the press in xx, yy and zz directions is the same. However,  when I add 
pressure on 2D MoS2, many errors or strange results happen. For example, 
1.  Error in routine ggen (41074):
 too many g-vectors
2.  the press has not been added judging from the outfile,  even though it has 
fininshed without err. 

Who can help me solve it? Or give me some suggestion on adding press on 2D 
materials.

Truely
P. L. Gong


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Re: [Pw_forum] Hubbard for oxygen

[Youssef]

Dear Mattioli,,

Normally we apply an infinitesimal value of U with a finite one for
alpha, do you mean that we do apply the converged value of U ( for
example 2.5 ev for W from conventional cell ) in stead, and continue
with standard procedure to determine the new U (U_out)??
  
-- 
Youssef Aharbil,
Laboratory of Physics and Chemistry of Materials
Faculty of sciences Ben msik, Casablanca
Morocco

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Re: [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  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
> 
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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.cant...@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



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Re: [Pw_forum] Hubbard for oxygen

[Giuseppe Mattioli]

Dear Youssuf
Sorry, I do not fully understand your question, so I try to answer but it might 
not be what you expect.
in my experience it is better to use a supercell to avoid spurious interactions 
between periodically replicated images of the U-perturbed atom. The 
response to the alpha perturbation is generally linear around the converged 
value (U_in=U_out), but when U_in is far from the converged value you may 
found a weird behavior. If you have a good U_out value coming from a unit-cell 
calculation and you are looking for a converged value with respect to 
the cell dimensions, then use such U_out value as U_in value in a supercell 
calculation (with k-points scaled to sample in the same, or very close way 
the Brillouin zone). You should see a shift of the new U-out value, depending 
on the different interaction between perturbed atoms in PBC. Try again to 
start with such U_out as U_in until you reach convergence (0.1 eV is generally 
enough for standard purposes). Then you may try again to extend the 
supercell and to check if your last U_out value is stable in the new system...
HTH

Giuseppe 

On Sunday, February 15, 2015 12:23:37 PM Youssef wrote:
> Dear Giuseppe,
> 
> Thank you very much for your help, I was really stuck.
> 
> I have another question about the linear response approach, in fact I
> successfully got the liner behavior of alpha=f(dn) and alpha=f(dn0) on
> conventional cell, with a very good value of U with respect to the
> literature, now when I move to supercell (2x2x2) the linearity is
> broken !!!
> 
> Any idea about this issue?
> 
> P.S: The convergence criterion's are well tested in addition to cell and
> atomic positions are relaxed


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