Real-time dynamics with external field read from file
In this tutorial we will see how to generate an external field in a format compatible with Lumen and then use it to run real-time simulation (see for instance Ref. [1].
We will also prove a simple python script to do it, that you can easily modify to create your own external field.
The tutorial is divided in three sections: 1) generate external field with YamboPy; 2) generate external field with ypp_rt; 3) use the external field in the real-time calculations.
Generate external field with YamboPy
In YamboPy you can find a tutorial to generate external field in the folder yambopy/tutorial/external_field/generate_field.pyYou can define your external field in this way:
def gauss_field(t_steps):
# In this example we generate a guassian external field
sigma=5.0*fs2aut # Field width
T_0 =3.0*sigma
Expf =np.exp(-(t_steps-T_0)**2/(2.0*sigma**2) )
a_t =sigma*np.sqrt(math.pi/2.0)*(special.erf((t_steps-T_0)/(sigma*np.sqrt(2.0)))+1.0)
ap_t =Expf
app_t=-Expf*(t_steps-T_0)/sigma**2
return a_t,ap_t,app_t
Just a function that generate a(t), a'(t), a(t) that will be then read from Yambo_rt/Yambo_nl. You can add you function to generate_field.pyscritp or use the two that are already implemented
SIN and GAUSS fields. Notice that the electric field correspond to E(t) = -E_amp a'(t).
The field amplitude (intensity) is not required because it will be read from the Yambo input.
Nota bene: only linear polarized external field can generated with YamboPY (to be generlized)
Generate external field with ypp_rt
With ypp_rt one can generate all external fields that implemented in the Yambo code in the file src/modules/mod_fields.F. This can be usefull to visualize external fields used in Yambo without the need of running a real simulation. However if you want to add a new external field you have to code it in the file src/modules/mod_fields.F. The command to generate external field on file is: ypp_rt -rtplot f. This will generate the following input file:
TDplots # [R] TD observables plot RTtime # [R] Post-Processing kind: function of time RTfields # [R] Analize time-dependent fields TimeStep= 0.010000 fs # Time step % TimeRange 0.000000 |100.000000 | fs # Time-window where processing is done % % EnRngeRt 0.00000 | 20.00000 | eV # Energy range % ETStpsRt= 200 # Total Energy steps ChirpFac= 0.000000 fs # Prefactor for linear chirping in frequency space Field1_Freq= 2.000000 eV # [RT Field1] Frequency Field1_Int= 1000.000000 kWLm2 # [RT Field1] Intensity Field1_Width= 0.000000 fs # [RT Field1] Width Field1_kind= "SIN" # [RT Field1] Kind(SIN|COS|RES|ANTIRES|GAUSS|DELTA|QSSIN) Field1_pol= "linear" # [RT Field1] Pol(linear|circular) % Field1_Dir 1.000000 | 0.000000 | 0.000000 | # [RT Field1] Versor % Field1_Tstart= 0.010000 fs # [RT Field1] Initial Time
In the input file you have to specify a series of parameters, in red: the time step (TimeSpep), the time range (TimeRange), the field intensity (Field1_Int), the field kind (Field1_kind), its polarization, the field direction (Field1_Dir) and its starting time (Field1_Tstart), usually the first step of the dynamics. Then you run ypp_rt with this input and it will produce a series of files: YPP_EXTFIELD1_P1.time, YPP_EXTFIELD1_P2.time, YPP_EXTFIELD1_P1.freq, YPP_EXTFIELD1_P2.freq.
These files contain the external field and its Fourier transform. In the next section we will see how to use them in real-time dynamics.
Use generated external field with yambo_rt/yambo_nl
In yambo_rt/yambo_nl you can tell to the code to read an external field from file. For example in yambo_nl you generate your input wil the command yambo_nl -u p
nloptics # [R] Non-linear spectroscopy % NLBands 7 | 10 | # [NL] Bands range % NLverbosity= "high" # [NL] Verbosity level (low | high) NLtime=100.000000 fs # [NL] Simulation Time NLintegrator= "INVINT" # [NL] Integrator ("EULEREXP/RK2/RK4/RK2EXP/HEUN/INVINT/CRANKNIC") NLCorrelation= "IPA" # [NL] Correlation ("IPA/HARTREE/TDDFT/LRC/LRW/JGM/SEX/LSEX/LHF") NLLrcAlpha= 0.000000 # [NL] Long Range Correction NLDamping= 0.200000 eV # [NL] Damping (or dephasing) RADLifeTime=-1.000000 fs # [RT] Radiative life-time (if negative RADLifeTime=Phase_LifeTime) #EvalCurrent # [NL] Evaluate the current HARRLvcs= 11529 RL # [HA] Hartree RL components EXXRLvcs= 11529 RL # [XX] Exchange RL components CORRLvcs= 11529 RL # [GW] Correlation RL components Field1_Freq= 0.100000 eV # [RT Field1] Frequency Field1_Int= 1000.00 kWLm2 # [RT Field1] Intensity Field1_Width= 0.000000 fs # [RT Field1] Width Field1_kind= "FROM_FILE ./YPP_EXTFIELD1_P1.time" # [RT Field1] Kind(SIN|COS|RES|ANTIRES|GAUSS|DELTA|QSSIN) Field1_pol= "linear" # [RT Field1] Pol(linear|circular) % Field1_Dir 1.000000 | 0.000000 | 0.000000 | # [RT Field1] Versor %
You have to specify the file kind FROM_FILE and give the path of the file containing the external field. Do not forget also to specify the NLtime and the Field1_Dir versor.
Nota bene: that external field from file in yambo_nl is compatible only with the INVINT integrator. (It will be generalized to other integrators soon)
References
- ↑ D. Sangalli, Excitons and carriers in transient absorption and time-resolved ARPES spectroscopy: An ab initio approach, Phys. Rev. Materials 5, 083803, (2021).
