[QE-users] some queries about mono layer optimization and vacuum

[rekha sharma]

Dear Sir,
Thanks for your reply.
It is very useful for me.
Consider my apology for late reply as my computer was not free.

ecutrho 52 is by mistake. actually it is 520 (uspp).

I tried to run calculations for "V" but I could not finish pp.x.
I run pw.x followed by pp.x.

my pp.in is

&inputPP
   prefix = 'pwscf'
   outdir='/tmp-$i',
   plot_num=11
   filplot = 'pp-$i.pot'
/

&plot
   iflag=3,
   output_format=5
/

where prefix and outdir is same as I used in in my scf file.

I am getting below xml error

   Error in routine pw_readschemafile (1):
     xml data file not found
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

     stopping ...

 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
     Error in routine pw_readschemafile (1):
     xml data file not found
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

     stopping ..

Please suggest me how to run pp.x.

My problem is related with  this issue
<https://lists.quantum-espresso.org/pipermail/users/2017-November/039771.html>
but I am not doing any restart_mode calculation.


Best Wishes,

Rekha



On Thu, Jan 2, 2020 at 6:50 PM Lucas Nicolás Lodeiro Moraga <
lucas.lodeiro at ug.uchile.cl> wrote:

> Hello Rekha!
> I am not an expert in monolayers, I work with slabs, but the problems
> should be similar.
> First, the ecutrho value that you use (52) it is very low... I do not know
> wich type of pseudopotential do you use (NormConserving, UltraSoft, PAW),
> but the ecutrho must be 4 times the ecutwfc (For US and PAW form 6 to 12
> times). Other thing, the convergence criteria of 1meV its good, but I
> prefer a criteria independent of number of atoms, as 1meV/atom... If you
> have the same system with more atoms, with your criteria you need a higher
> values to reach ir, but if use an independent atoms criteria, the values
> are the same for small and big systems.
>
> MONOLAYER:
> kpoints: I use 1 point in the vacuum direction, and I do not found any
> difference when I use 2 or more kpoints in this direction. The bands
> dispersion in this direction is negligible.
> cell: The 2Dshape flag does not change your cell because it does not
> change the xy area, how you have an orthogonal a,b vectors and a=b. The
> broken of this symmetry is energetically not allowed. For this, 2Dxy flag
> works and minimize the cell in xy directions, and reduce the stress.
> If is it okay the parameters deviates from the bulk? I do not know for the
> case of Monolayers... but for me makes sense, in your calculation the xy
> area reduces to maximize the interaction with the neighborhood. If you want
> do a vc-relax the 2Dxy is the correct flag.
> Vacuum: 30 bohr should be enough... In my systems I do a similar vacuum
> test, and 30 bohr gives the same result as 200 bohr.
> I guess your system have charged surfaces, dipoles or something like that.
> If is a bynary semiconductor AB... a monolayer gives you a "A type" and a
> "B Type" surfaces, how A and B have different electronegativities, exists a
> dipole between both surfaces, that could explain the energy behaviour with
> vacuum.
> I recommend, do a post-processing calculation for the monolayer, calculate
> the electrostatic potential (V) along the vacuum direction... If V is not
> plane in the vaccum region, do you have a dipole on the monolayer. You can
> fix it using a dip-field on the vacuum... with it you add a "V step" on the
> vacuum, giving you two V planes on vaccum, "two types of vaccum".
> Other way, is making a monolayer with equal surfaces, like A-A or B-B
> (adding a plane of atoms)... this fix the dipole in most cases... but I do
> not know if this is still a monolayer or what you want.
>
> Regards
>
> Lucas Lodeiro
>
>

-- 




Best wishes

Ms. Rekha
Ex-PG student,
LBS college, Jaipur
India
Mob.: +11 90-95 790 71 697
Email: rekha1997jpr at gmail.com
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