Circular Dichroism

[sunxl]

Dear all，

1、Recently, I came across the calculation of circular dichroism for isolated molecules in the Yambo tutorial https://wiki.yambo-code.eu/wiki/index.p ... _molecules. The guidance provided was only about the general input parameter settings. I would like to know if there are any detailed tutorials available, such as instructions on how to generate the input file using which command, and which executable file to run the calculation. Additionally, I would like to ask if I want to calculate the CD of a one-dimensional periodic chain, does it suffice to simply change the Coulomb cutoff based on the isolated molecule tutorial?

2、Did Yambo successfully perform the SHG calculation for both left-handed and right-handed circularly polarized light? The relevant content in the SHG calculation input file is as follows:

% Field1_Freq
0.100000 | 0.100000 | eV # [RT Field1] Frequency
%
Field1_NFreqs= 1 # [RT Field1] Frequency
Field1_Int= 1000.00 kWLm2 # [RT Field1] Intensity
Field1_Width= 0.000000 fs # [RT Field1] Width
Field1_kind= "SOFTSIN" # [RT Field1] Kind(SIN|COS|RES|ANTIRES|GAUSS|DELTA|QSSIN)
Field1_pol= "linear" # [RT Field1] Pol(linear|circular)
% Field1_Dir
0.000000 | 0.000000 | 0.000000 | # [RT Field1] Versor
%

If I am calculating a one-dimensional chain where the z-direction is the periodic direction, then should I set up

Field1_pol= "circular" # [RT Field1] Pol(linear|circular)
% Field1_Dir
0.000000 | .000000 | 1.000000 | # [RT Field1] Versor

Then, by changing Field1_Dir = 0 0 1 and 0 0 -1, the right-circularly polarized light and the left-circularly polarized light can be set. Are there any other settings that need to be emphasized or changed?


Best,
sunxl

[Davide Sangalli]

Dear Sunxl,

1、Recently, I came across the calculation of circular dichroism for isolated molecules in the Yambo tutorial https://wiki.yambo-code.eu/wiki/index.p ... _molecules. The guidance provided was only about the general input parameter settings. I would like to know if there are any detailed tutorials available, such as instructions on how to generate the input file using which command, and which executable file to run the calculation. Additionally, I would like to ask if I want to calculate the CD of a one-dimensional periodic chain, does it suffice to simply change the Coulomb cutoff based on the isolated molecule tutorial?

Yes and no. It will work, however, since 1D is periodic, you will end up facing the issue of having intra-band dipoles which in PBC are not well defined (see brief discussion in the tutorial and in the cited reference)

2、Did Yambo successfully perform the SHG calculation for both left-handed and right-handed circularly polarized light? The relevant content in the SHG calculation input file is as follows:

Not sure I understand what you mean here. However, for performing real-time simulations with circularly polarized laser pulses, you can use the following input

Code: Select all

Field1_pol= "circular" # [RT Field1] Pol(linear|circular)
% Field1_Dir
0.000000 | .000000 | 1.000000 | # [RT Field1] Versor
%
% Field1_Dir_circ
0.000000 | 1.000000 | 0.000000 | # [RT Field1] Versor_Circ
%

In practice the "circular" option for the field, means the total pulse is constructed superimposing two linearly polarized pulses de-phased by pi/2. All options are shared but the polarization directions, for which you have Field1_Dir and Field1_Dir_Circ. If you set the two orthogonal you get a circularly polarized pulse. In the example in the yz plane. By changing the polarization of one of the two from +1 to -1 you will switch from plus to minus circular polarization. Please notice that, for now, many developments connected to the yambo_nl executables are done inside the Lumen fork (https://www.lumen-code.org/) of yambo

Best,
D.