[Pw_forum] Dielectric Constant Using Phonon

[Marton]

Hi Kanak,

Does your system contain three layers of MoS2 and some vacuum along z? If
yes, then the high frequency dielectric constant will approach 1 as you
increase the size of the vacuum or in other words the interlayer separation.

There is a nice discussion why this should happen for example in

http://journals.aps.org/prb/abstract/10.1103/PhysRevB.88.245309

In particular, check Fig.7. and the related section.

Sincerely,
Marton Voros

--
Aneesur Rahman Fellow
Materials Science Division
Argonne National Laboratory

On Tue, Feb 2, 2016 at 3:45 AM, Kanak Datta <kanakeee08 at gmail.com> wrote:

> Dear researchers
>
> I have been trying to calculate the dielectric constant of multilayer TMDC
> materials. I have used the ph.x package of quantum espresso for this. From
> simulation I have got the following values:
>
>   Dielectric constant in cartesian axis
>
>           (       6.990898310       0.000000000       0.000000000 )
>           (       0.000000000       6.990898310       0.000000000 )
>           (       0.000000000       0.000000000       1.520000669 )
>
> The values were obtained for Mos2 trilayer. I did the scf calculation
> before using the phonon package. The following code was used for phonon:
>
> &inputph
>   tr2_ph=1.0d-14,
>   prefix='MoS2AAA187',
>   epsil=.true.
>   outdir='D:\Quantum ESPRESSO 64-bit 5.1.2-mpich2\MoS2AAA187\outdir',
>   !outdir='./'
>   fildyn='MoS2AAA187.dynG',
>
>  /
>  0.0 0.0 0.0
>
> For scf calculation I used pbe-hgh pseudopotentials.
> The question is, why the z axis value of dielectric constant is so low?
> Values found in the literature is typically close. Is there something that
> must be added in phonon package?
>
> Thanks in advance.
>
> Sincerely yours
> Kanak
> EEE, BUET
>
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