[QE-users] about the option "assume_isolated=2D"

[Juliana Morbec]

Dear all.

I have been trying to compute the band edge of 2D TMDCs and I have tested
the option with and without "assume_isolated=2D". I noticed that this flag
strongly affects the positions of the band edges. For example, the VBM/CBM
of MoS2 change from -5.93/-4.20 eV with "assume_isolated=2D" to -4.96/-3.23
eV without "assume_isolated=2D"; all values were computed with respect to
the vacuum level, which is 0 eV in the first case and 0.08 eV in the second
case; I used a quite significant vacuum area in the calculatons (~90 Ang).

I read the paper "Density functional perturbation theory for gated
two-dimensional heterostructures: Theoretical developments and application
to flexural phonons in graphene" by  Sohier, Calandra add Mauri (Physical
Review B 96, 75448), and I understood that the new method would make
differences if one wants to investigate charged 2D materials, e.g. with
charged defect, or 2D materials in a perpendicular electric field, but not
in the case of pure MoS2, no charge, no field. I do not understand why such
a large difference in the case of pure 2D layers.

I will appreciate if someone could comment on this.

Thank you for your time.

Best regards,

Juliana Morbec
-- 
Juliana Morbec, PhD
Research Associate - Prof. Kratzer's group
University of Duisburg-Essen, Germany
https://jmmorbec.wordpress.com/
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