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

[rekha sharma]

I could finish a test case.
I need to define some variables in qe.in file.

Will get back to you once I finish it.

Thank you sir,

best wishes

Rekha

On Sat, Jan 4, 2020 at 2:08 PM rekha sharma <rekha1997jpr at gmail.com> wrote:

> 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
>


-- 




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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