Pump and Probe

This tutorial works only with Yambo version > 5.5, that will be released soon.

In this tutorial we will show you how to setup two external fields in yambo_nl, to perform pump and probe simulation.
The input simulation parameters of these tutorial require large computational power, we advice you to run them in parallel, or to use simplified parameters for example less bands, k-points and so on. This tutorial supposes that you are already familiar with real-time simulation with Yambo, if it is not the case please check these tutorials: Tutorials#Non_linear_response

We start from the h-BN monolayer with an in place lattice constant a=2.5 Å and a box large 30 a.u. in the z-direction. Standard DFT input for hBN monolayer for ABINIT or QuantumEspresso can be found here Tutorials.
We used a 24x24x1 k-points grid and 100 bands in the non-self consistent calculation. In order to have faster calculation we advice you to decrease the k-points grid to 12x12x1, results will be very close to the converged ones.

In our example we choose direction [0,1,0] for the pump and the probe. We generate the ypp.in to remove symmetries with the command ypp -y and we modify it as:

fixsyms                          # [R] Remove symmetries not consistent with an external perturbation
% Efield1
 0.000000 | 1.000000 | 0.000000 |        # First external Electric Field
%
% Efield2
 0.000000 | 1.000000 | 0.000000 |        # Additional external Electric Field
%
BField= 0.000000           T     # [MAG] Magnetic field modulus
Bpsi= 0.000000             deg   # [MAG] Magnetic field psi angle [degree]
Btheta= 0.000000           deg   # [MAG] Magnetic field theta angle [degree]
#RmAllSymm                     # Remove all symmetries 
RmTimeRev                     # Remove Time Reversal
#RmSpaceInv                    # Remove Spatial Inversion

then we go in the FixSymm directory and run again the setup. Now we calculate collisions, since we want to include excitonic effects in the calculations. Using the command: yambo_nl -v h+sex+cvonly -e -X s -r:

collisions                       # [R] Collisions
em1s                             # [R][Xs] Statically Screened Interaction
dipoles                          # [R] Oscillator strenghts (or dipoles)
DIP_Threads=0                    # [OPENMP/X] Number of threads for dipoles
X_Threads=0                      # [OPENMP/X] Number of threads for response functions
RT_Threads=0                     # [OPENMP/RT] Number of threads for real-time
RandQpts=  30000000               # [RIM] Number of random q-points in the BZ
RandGvec= 1                RL    # [RIM] Coulomb interaction RS components
CUTGeo= " box Z"                  # [CUT] Coulomb Cutoff geometry: box/cylinder/sphere/ws/slab X/Y/Z/XY..
% CUTBox
 0.00000 |  0.00000 |  29.50000 |        # [CUT] [au] Box sides
%
Chimod= "HARTREE"                # [X] IP/Hartree/ALDA/LRC/PF/BSfxc
% BndsRnXs
   1 | 100 |                         # [Xs] Polarization function bands
%
NGsBlkXs=   10000 mHa     # [Xs] Response block size
% LongDrXs
 0.000000 | 1.000000 | 0.000000 |        # [Xs] [cc] Electric Field
%
XTermKind= "BG"                # [X] X terminator ("none","BG" Bruneval-Gonze)
% COLLBands
   5 | 12 |                          # [COLL] Bands for the collisions
%
HXC_Potential= "SEX+HARTREE+CVONLY" # [SC] SC HXC Potential
HARRLvcs= 10000 mHa   # [HA] Hartree     RL components
EXXRLvcs= 10000 mHa    # [XX] Exchange    RL components
CORRLvcs= 10000 mHa    # [GW] Correlation RL components