## How to obtain the transient reflectivity/absorption using Yambo

Deals with issues related to computation of optical spectra, in RPA (-o c) or by solving the Bethe-Salpeter equation (-o b). Includes local field effects, excitons, etc.
Bramhachari Khamari
Posts: 69
Joined: Wed Oct 23, 2019 5:52 am

### How to obtain the transient reflectivity/absorption using Yambo

Dear Developers,
I am keen to learn the the calculation of transient reflectivity or absorption using YAMBO code. To learn that I am following a paper (https://journals.aps.org/prb/abstract/1 ... .93.195205) on bulk silicon where the transient reflectivity is calculated using Bethe Salpeter level as implemented in Yambo.  I could obtain the following

i) I could reproduce  the  G0W0+BSE spectrum first
ii) Then I did a real time approach to obtain the optical spectrum which looks like as obtained from BSE. Following input is used for real time simulation

Yambo_rt -q p gives

negf # [R] Real-Time dynamics
HXC_Potential= "HARTREE+SEX" # [SC] SC HXC Potential
GfnQPdb= "E < SAVE/ndb.QP" # [EXTQP G] Database
GfnQP_N= 1 # [EXTQP G] Interpolation neighbours
% GfnQP_E
0.000000 | 1.000000 | 1.000000 | # [EXTQP G] E parameters (c/v) eV|adim|adim
%
GfnQP_Z= ( 1.000000 , 0.000000 ) # [EXTQP G] Z factor (c/v)
GfnQP_Wv_E= 0.000000 eV # [EXTQP G] W Energy reference (valence)
% GfnQP_Wv
0.00 | 0.00 | 0.00 | # [EXTQP G] W parameters (valence) eV| 1|eV^-1
%
GfnQP_Wv_dos= 0.000000 eV # [EXTQP G] W dos pre-factor (valence)
GfnQP_Wc_E= 0.000000 eV # [EXTQP G] W Energy reference (conduction)
% GfnQP_Wc
0.00 | 0.00 | 0.00 | # [EXTQP G] W parameters (conduction) eV| 1 |eV^-1
%
GfnQP_Wc_dos= 0.000000 eV # [EXTQP G] W dos pre-factor (conduction)
% RTBands
4 | 5 | # [RT] Bands
%
Integrator= "RK2" # [RT] Integrator. Use keywords space separated ( "EULER/EXPn/INV" "SIMPLE/RK2/RK4/HEUN" "RWA")
PhLifeTime= 0.000000 fs # [RT] Dephasing Time
RTstep=10.000000 as # [RT] Real Time step length
NETime=55.000000 fs # [RT] Simulation Time
% IOtime
0.05 | 0.10 | 0.10 | fs # [RT] Time between to consecutive I/O (OBSERVABLEs,CARRIERs - GF - OUTPUT)
%
% Field1_Freq
0.00 | 0.00 | eV # [RT Field1] Frequency
%
Field1_Int=1000.000000 kWLm2 # [RT Field1] Intensity
Field1_Width= 0.000000 fs # [RT Field1] Width
Field1_kind= "DELTA" # [RT Field1] Kind(SIN|RES|ANTIRES|GAUSS|DELTA|QSSIN)
Field1_pol= "linear" # [RT Field1] Pol(linear|circular)
% Field1_Dir
0.000000 | 1.000000 | 0.000000 | # [RT Field1] Versor
%
% Field1_Dir_circ
0.000000 | 0.000000 | 0.000000 | # [RT Field1] Versor_circ
%
Field1_Tstart= 0.010000fs # [RT Field1] Initial Time

However, I don not know how to set the parameter for pumb probe set up with a time delay using yambo to obtain the transient spectrum. I did not find any tutorials which talks about this. Can anybody help me in this regard.

Regards,
Bramhachari Khamari
Bramhachari Khamari
Post Doctoral Fellow
Department of Physics
IIT Kanpur, India.

Davide Sangalli
Posts: 376
Joined: Tue May 29, 2012 4:49 pm
Location: Via Salaria Km 29.3, CP 10, 00016, Monterotondo Stazione, Italy
Contact:

### Re: How to obtain the transient reflectivity/absorption using Yambo

Dear Bramhachari Khamari,
unfortunately the part of the code for describing pump and probe experiments is not yet included in the GPL release.

It will be likely included in future releases, but we do not know yet when.
One of the reasons is that, before being released, the code needs to be improved, made user friendly, and extended to work in all cases.

Kind regards,
D.
Davide Sangalli, PhD
CNR-ISM, Division of Ultrafast Processes in Materials (FLASHit) and MaX Centre
http://www.oldism.cnr.it/en/davide-sangalli-cv/
http://www.max-centre.eu/

Bramhachari Khamari
Posts: 69
Joined: Wed Oct 23, 2019 5:52 am

### Re: How to obtain the transient reflectivity/absorption using Yambo

Dear Sir,
Thank you for the reply. Now, I could generate the inputs with two fields. Here is the input generated for Si using yambo-4.4 . I would like to clarify few points,
i) Can I take Field1 and Field2 as pump and probe field respectively.

ii) Using start time (Field1_Tstart and Filed2_Tstart), can we set the delay between the field by setting Field2_Tstart to some value

iii) If I get a spectrum by post processing, can we think of it as a spectrum corresponds to a time delay fixed by Field2_Tstart.

% Field1_Freq
3.26 | 3.26 | eV # [RT Field1] Frequency
%
Field1_Int=1000.000000 kWLm2 # [RT Field1] Intensity
Field1_Width=43.000000 fs # [RT Field1] Width
Field1_kind= "GAUSS" # [RT Field1] Kind(SIN|RES|ANTIRES|GAUSS|DELTA|QSSIN)
Field1_pol= "linear" # [RT Field1] Pol(linear|circular)
% Field1_Dir
0.000000 | 1.000000 | 0.000000 | # [RT Field1] Versor
%
% Field1_Dir_circ
0.000000 | 0.000000 | 0.000000 | # [RT Field1] Versor_circ
%
Field1_Tstart= 0.010000fs # [RT Field1] Initial Time
% Field2_Freq
3.26 | 3.26 | eV # [RT Field2] Frequency
%
Field2_Int=100.000000 kWLm2 # [RT Field2] Intensity
Field2_Width=20.000000 fs # [RT Field2] Width
Field2_kind= "GAUSS" # [RT Field2] Kind(SIN|RES|ANTIRES|GAUSS|DELTA|QSSIN)
Field2_pol= "linear" # [RT Field2] Pol(linear|circular)
% Field2_Dir
0.000000 | 1.000000 | 0.000000 | # [RT Field2] Versor
%
% Field2_Dir_circ
0.000000 | 0.000000 | 0.000000 | # [RT Field2] Versor_circ
%
Field2_Tstart=400.000000fs # [RT Field2] Initial Time

Regards,
Bramhachari Khamari
Bramhachari Khamari
Post Doctoral Fellow
Department of Physics
IIT Kanpur, India.

Davide Sangalli
Posts: 376
Joined: Tue May 29, 2012 4:49 pm
Location: Via Salaria Km 29.3, CP 10, 00016, Monterotondo Stazione, Italy
Contact:

### Re: How to obtain the transient reflectivity/absorption using Yambo

In principle yes. The spectrum would be obtained from the polarization at the time difference T1_start - T2_start and then one should remove the polarization/spectrum with just one field.

I never tried that, but I do not see why it should not work.
Davide Sangalli, PhD
CNR-ISM, Division of Ultrafast Processes in Materials (FLASHit) and MaX Centre
http://www.oldism.cnr.it/en/davide-sangalli-cv/
http://www.max-centre.eu/

Bramhachari Khamari
Posts: 69
Joined: Wed Oct 23, 2019 5:52 am

### Re: How to obtain the transient reflectivity/absorption using Yambo

Dear Sir,
Thank you so much for the reply. I will follow this procedure and try to obtain the spectrum for the Si. I will contact you again, if I face any further difficulty.

Regards,
Bramha
Bramhachari Khamari
Post Doctoral Fellow
Department of Physics
IIT Kanpur, India.

Bramhachari Khamari
Posts: 69
Joined: Wed Oct 23, 2019 5:52 am

### Re: How to obtain the transient reflectivity/absorption using Yambo

Dear Sir,
I run real time simulation for the Si by applying two fields. I have few doubts which are mentioned as follows

i) The frequency of the first field is set as excitation frequency obtained form the BSE calculation. What will be the frequency for Field2 and its polarisation direction. Could you explain how to choose parameters related to field2 i.e intensity, the polarisation direction of the Field2 with respect to Field1

ii) Why the out put has information related to field1 but not about Field2, although in my input file both are set.

iii) How do I get the information about the carriers that are generated by the pump pulse Field1, so that I can plot variation of carriers as a function of time

Here is the input and output file
####################################################
% Field1_Freq
3.26 | 3.26 | eV # [RT Field1] Frequency
%
Field1_Int=1000000000.000000 kWLm2 # [RT Field1] Intensity
Field1_Width=43.000000 fs # [RT Field1] Width
Field1_kind= "GAUSS" # [RT Field1] Kind(SIN|RES|ANTIRES|GAUSS|DELTA|QSSIN)
Field1_pol= "linear" # [RT Field1] Pol(linear|circular)
% Field1_Dir
0.000000 | 1.000000 | 0.000000 | # [RT Field1] Versor
%
% Field1_Dir_circ
0.000000 | 0.000000 | 0.000000 | # [RT Field1] Versor_circ
%
Field1_Tstart= 0.010000fs # [RT Field1] Initial Time
% Field2_Freq
3.26 | 3.26 | eV # [RT Field2] Frequency
%
Field2_Int=100.000000 kWLm2 # [RT Field2] Intensity
Field2_Width=20.000000 fs # [RT Field2] Width
Field2_kind= "GAUSS" # [RT Field2] Kind(SIN|RES|ANTIRES|GAUSS|DELTA|QSSIN)
Field2_pol= "linear" # [RT Field2] Pol(linear|circular)
% Field2_Dir
0.000000 | 0.000000 | 0.000000 | # [RT Field2] Versor
%
% Field2_Dir_circ
0.000000 | 0.000000 | 0.000000 | # [RT Field2] Versor_circ
%
Field2_Tstart=400.010000fs # [RT Field2] Initial Time
######################################################################
The output in the r_negf reads as follows

---I/O---
T between I/O of OBS [fs]: 0.100000
I/O of GFs [fs]: 0.100000
outputs [fs]: 0.100000
Extended collisions [I/O]:yes

---Fields---
Gauge :length
Field1 field :GAUSS
Field1 polarization :linear
Field1 energy window/period [eV/fs]: 3.2600000 3.2600000 1.2686096 1.2686096
Field1 elemental oscillation [fs]: 0.0000000
Field1 width [fs]: 43.000000
Field1 energy steps : 1
Field1 electric field [V/m]:0.1941E+10
Field1 max intensity [kW/cm^2]:0.1000E+10
Field1 max fluence [nJ/cm^2]:0.76214E+8
Field1 final time [fs]: 258.10000
Field1 half maximum full width [fs]: 101.25726
#####################################################

Regards,
Bramhachari Khamari
Bramhachari Khamari
Post Doctoral Fellow
Department of Physics
IIT Kanpur, India.