Born effective charges

[marmotte]

Dear all,

Should the calculated values fulfill the acoustic sum rule \sum_s Z_{s,ij}^*=0 ?

I'm finding a huge number like 6 ? is it a problem of relaxation or strained structure ? I did calculation from the experimental structure.

Thank you

[Troels Markussen]

Hi,

The acoustic sum rule should ideally be fulfilled. It should be OK to use the experimental structure. I would suggest that you try to decrease the displacement of the atoms (delta_z in the tutorial http://quantumwise.com/documents/tutorials/latest/Polarization/index.html/chap.born.html), if you didn't already try that.

Troels

[Kim_W]

How to get accurate value of born effective charges for 2D materials (e.g. graphene, single layer black phosphorus etc.).  The result was changed with different vacuum spacing.

[Ulrik G. Vej-Hansen]

Please provide the python script(s) you have used and a more detailed explanation of what you have tried and how it differed from your expectations.

[Kim_W]

When I changed the value of c in GaN.nc script, the value of BEC was also changed slightly. Besided,  the result of my calculation is different from the previous reports of 3.08-3.23.

[Ulrik G. Vej-Hansen]

Thanks, I will look into it and get back to you.

[Ulrik G. Vej-Hansen]

Unfortunately, our current implementation is only guaranteed to work for orthogonal cells, as stated in this tutorial on polarization: https://docs.quantumwise.com/tutorials/polarization/polarization.html

I am sorry for any inconvenience this has caused, and I will make sure that we update the manual page to make this clearer.

[Kim_W]

Thank you a lot. Then, I try to turn the lattice into orthogonal cell use surface(cleave) tool, however, the result is also different from the previous reports. Can you help me?

[Ulrik G. Vej-Hansen]

I will have a look at the scripts and get back to you.

[Ulrik G. Vej-Hansen]

Could you provide the source for the reference numbers you quote, please?

[Kim_W]

[1] Computational discovery of single-layer III-V materials
[2] GaN: From three- to two-dimensional single-layer crystal and its multilayer van der Waals solids

[Ulrik G. Vej-Hansen]

Please provide the direct reference or the DOI, so I can find them. The title alone is not adequate for academic papers.

[Kim_W]

 DOI: 10.1103/PhysRevB.87.165415
 DOI: 10.1103/PhysRevB.93.085431

[Ulrik G. Vej-Hansen]

Thanks, I will take a look at them.

On closer inspection of the script, I have realized that you have simply copied the one from the tutorial directly, without modifying it. Please go back and read through the tutorial in detail, so you understand how the script is created. This should allow you to modify it to suit the 2D system you are interested in.

[Kim_W]

The question is: How to set the length of lattice vector in z-direction when calculate the BEC for 2D materials?