difference of dielectric function between 4.5 and 4.2

[yhypku]

Dear all,
I ran a BSE of 2D hBN in 4.2 last year and ran the same job using the same parametes in 4.5 recently. I used L=3.33A and got Reeps(0)=3.85 in 4.5 while in 4.2 the value is 1.6. I was confused what L should be chosen to make the dielectric function the same for the two version. Could you please tell me the difference of this between the two version in details? Thanks very much.
Best,
Huaiyuan

[Daniele Varsano]

Dear Huaiyuan,

you should post the reports and outputs of the two calculation to look into it carefully. Anyway, what changed was surely the way to treat low dimensional systems (2D) when using a coulomb cutoff potential. Note that in a 2D system eps it is not well defined (it depends on the volume of the supercell) and what you should look at, it is the value of the polarizability alpha.

Best,
Daniele

[yhypku]

Dear Daniele:
Here are my output. First is the output of 4.2. I only post the value at E=2.
# E/ev[1] EPS-Im[2] EPS-Re[3] EPSo-Im[4] EPSo-Re[5]
#
2.000 0.7789E-2 1.612 0.1871E-2 1.381
Then is the output of 4.5.
# E/ev[1] ALPHA-Im[2] ALPHA-Re[3] ALPHAo-Im[4] ALPHAo-Re[5]
#
2.0040 0.0205 1.6079 0.0049 1.0009
The vaccum thickness of my 2D BN is 33 au. I try to use the formula: \eps=4 * \pi * \alpha / L + 1 but I don't know how to set the value of L. Could you please tell me the right way to get the eps from alpha? Thanks in advance.
Best,
Huaiyuan

[Daniele Varsano]

Dear Huaiyuan,
this is useless, can you post the report and output files? you can attach them using the attachments button, you will need to rename the file in an allowed format (e.g. txt, or zip).
Best,
Daniele

[yhypku]

Dear Daniele:
I found that I should set L=33au(vaccum thickness). Thanks for your patience.
Best,
Huaiyuan