# Lumen code is online!

My code to calculate non-linear response in solids and nanostructure is finally online.
The first tutorials are available, and soon I will finish the other ones.
Full free to use it and let me know if you find bugs or strange things.

## 5 thoughts on “Lumen code is online!”

1. WENSHEN SONG

Hello,
I try to do SHG calculation in lumen, but I cannot find a forum for lumen so I ask questions here. I wonder how to set the direction for the SHG tensor chi. As far as I am concerned, Chi_ijk could be expressed as P_i=Chi_ijk E_j E_k, so how can we determine the i,j and k in lumen? I read the tutorial for lumen SHG in AlAs, and the external field is set as
ExtF_Dir
1.000000 | 1.000000 | 0.000000 |

Does it mean setting j=x and k=y? And the output for x,y,z directions should give Chi_xxy, Chi_yxy, Chi_zxy? If so, why does the tutorial plot give a label as Chi_xyz?

1. attacc Post author

Dear Wenshen

thank you for interesting in Lumen.
I will add a Forum to Lumen soon ðŸ™‚
>
> I wonder how to set the direction for the SHG tensor chi. As far as I am concerned, Chi_ijk could be expressed as P_i=Chi_ijk E_j E_k. So, how can we determine the i,j and k in lumen? I read the tutorial for lumen SHG in AlAs, and the external field is set as
> ExtF_Dir
> 1.000000 | 1.000000 | 0.000000 |

in this example there is only one field, therefore E_j=E_k.

> Does it mean setting j=x and k=y?
Yes the three numbers in the input are the x,y z direction, I modified the tutorial to make it clear

> And the output for x,y,z directions should give Chi_xxy, Chi_yxy, Chi_zxy? If so, why does the tutorial plot give a label as Chi_xyz, for which should actually be Chi_zxy?
In this example we calculate Chi_zxy but in AlAs Chi_zyx=Chi_xyz=Chi_yxz
see also Eq. 24 in https://journals.aps.org/prb/abstract/10.1103/PhysRevB.82.235201
I modified the tutorial to make this point clearer this point and corrected the figure

Yours
Claudio

2. Espirid

Hi.
I made a new post in the Lumen forum, however I have not received any response, I apologize if my attempt to find an answer here is too much.

I have tried to make a calculation of SHG, however I have reached a limit with the following error.
.
.
[ERROR] STOP signal received while in: [04.01] Initialization
[ERROR] Spin-polarized systems not fully implemented

Unfortunately I can not ignore the polarization of the spin, so I would like to know if someone has a hint or a way to solve such a situation.

Greetings and thanks for your time.

1. attacc Post author

Dear Espirid

unfortunatelly the spin-polarization at present the spin-polarization is not implemented in Lumen.
It should not be difficult to generalize it to the spin-polarized case, but I have no
time to work on it, at least this month.
You can try to have a look, and I can help you, or we can discuss in April of possible implementations.

Best
Claudio Attaccalite

1. Espirid

Thank you very much for your prompt response.
Unfortunately my knowledge in programming is not very good, even so I think I will try to check and see if I am lucky with the implementation.
Could you tell me where to attack code?

Thank you very much for your time to appreciate it.

regards

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