Wrong SHG component in nl calculations

[Dean]

Dear all,
I want to calculate the SHG coefficient of 2D material with C2v point group.
According to some references, one of non-zero SHG coefficient of this 2D materials is Xxxy.
But, my results show that the Xyyy is non-zero?
Any help is appreciated.
The input /output of QE and yambo are attached.
Best wishes,

[claudio]

Dear Dean

it seems that your result is just noise,
I don't know why, please try:

1) download the last version of the code
https://www.yambo-code.eu/2023/09/08/yambo-release-5-2/

2) decrease the time-step to 0.01 fs

3) increase the dephasing time miltiplayer in src/modules/mod_nl_optics.F
integer, parameter :: DephMult=6
and recompile ypp_nl and yambo_nl
than use NLtime=-1 in input

4) try to make a test on a simpler system for example hBN monolayer, and see if it works
here DFT inputs
https://www.yambo-code.eu/wiki/index.ph ... -BSE_level

let us know
best
Claudio

[Dean]

Dear Claudio,
Thanks for your reply.
1. I use the lastest version of the code (Yambo-5.2.0), but the output files show "Version 5.1.0 Revision 22561 Hash (prev commit) 785b4fd6f".
2. Based on your suggestion, I recombile yambo with DephMult=6. Then, set time-step to 0.01 fs and NLtime=-1 in the input, but the output is as same as previous run.(please the attachment)
3.I have make a test for hBN, and it works.
4.For my 2D system with C2v point group，it should have five non-zero SHG components, i.e., yxx,yyy, yzz, xxy,zyz. I can get SHG components including yxx,yyy,yzz, and yxy,yyz. But, according to some references, yxy and yyz should be zero, and xxy and zyz should be non-zero, which makes me confused.
Best,

[claudio]

Dear Yimin

I will try to reproduce your results and let you know

best
Claudio

[Dean]

Dear Claudio,
Is there any progress in reproducing my results?
I have another question. The NL calculations can be speed up on GPUs, especially the time-consuming COLLISIONS calculations?
Best,

[claudio]

Dear Yimin

I reproduced your results, and it is clear that there is a bug with this system, I will try to solve it this week
and come back to you

for the COLLISIONS... I will ask to the other developers I did not optimized that part

best
Claudio

[claudio]

Dear Yimin

are you sure of the atomic positions in your input? from QE the system does not have many symmetries.
I slightly modified atomic positions to be more symmetric, but I think you should have the correct symmetries
already at the QE level.

I will make you know for the rest

best
Claudio

[claudio]

Dear Yimin

you can get the correct structure here:

https://backend.orbit.dtu.dk/ws/files/3 ... _Kruse.pdf
https://cmrdb.fysik.dtu.dk/c2db/row/Nb2 ... 127da2c220

I also noticed that this material is ferroelectric, I don't know if this can be the problem....

I will see

best
Claudio

[Dean]

Dear Claudio，
Thanks for your reply.
Actually, this material is ferroelectric and shows C2v point group. That is why it does not show many symmetries. Your modified structure is not ferroelectric, which is not the most stable state for this kind of materials.
So, may ferroelectric preperty result in the problem?
Bset,

[claudio]

Dear Dr. Yimin Ding

probably it is not a problem if is ferroeletric, but one has to check it

best
Claudio