This tutorial will show how to perform a simple real-time BSE calculation with Yambo 4.4 on hBN monolayer. DFT inputs are available here: QE_inputs or ABINIT_inputs. Follow the first 6 steps of the linear-response tutorial. Then generate the input file to calculate the collisions (see appendix of Phys. Rev. B 84, 245110):

em1s # [R Xs] Static Inverse Dielectric Matrix collisions # [R] Eval the extended Collisions dipoles # [R ] Compute the 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 Chimod= "HARTREE" # [X] IP/Hartree/ALDA/LRC/PF/BSfxc % BndsRnXs 1 | 40 | # [Xs] Polarization function bands % NGsBlkXs= 1000 mHa # [Xs] Response block size % DmRngeXs 0.10000 | 0.10000 | eV # [Xs] Damping range % % LongDrXs 1.000000 | 0.000000 | 0.000000 | # [Xs] [cc] Electric Field % % COLLBands 4 | 5 | # [COLL] Bands for the collisions % HXC_Potential= "HARTREE+SEX" # [SC] SC HXC Potential HARRLvcs= 1000 mHa # [HA] Hartree RL components EXXRLvcs= 1000 mHa # [XX] Exchange RL components CORRLvcs= 1000 mHa # [GW] Correlation RL componentsWith this input we calculate the HARTREE and SEX collisions integrals. Notice that the HARTREE term in principle can be calculate on the fly, but in this way it is more efficiend expecially for the non-linear response. Here one has to converge the cutoff for the Hartree and the Screened Exchange, usually

Then you generate the input for the linear response

nloptics # [R NL] Non-linear optics DIP_Threads=0 # [OPENMP/X] Number of threads for dipoles NL_Threads=0 # [OPENMP/NL] Number of threads for nl-optics % NLBands 4 | 5 | # [NL] Bands % NLverbosity= "low" # [NL] Verbosity level (low | high) NLstep= 0.0100 fs # [NL] Real Time step length NLtime= 55.00000 fs # [NL] Simulation Time NLintegrator= "CRANKNIC" # [NL] Integrator ("EULEREXP/RK2/RK4/RK2EXP/HEUN/INVINT/CRANKNIC") NLCorrelation= "SEX" # [NL] Correlation ("IPA/HARTREE/TDDFT/LRC/LRW/JGM/SEX") NLLrcAlpha= 0.000000 # [NL] Long Range Correction % NLEnRange 0.200000 | 8.000000 | eV # [NL] Energy range % NLEnSteps= 1 # [NL] Energy steps NLDamping= 0.10000 eV # [NL] Damping #UseDipoles # [NL] Use Covariant Dipoles (just for test purpose) #FrSndOrd # [NL] Force second order in Covariant Dipoles #EvalCurrent # [NL] Evaluate the current HARRLvcs= 1017 RL # [HA] Hartree RL components EXXRLvcs= 1074 mHa # [XX] Exchange RL components % ExtF_Dir 0.000000 | 1.000000 | 0.000000 | # [NL ExtF] Versor % ExtF_Int= 1000. kWLm2 # [NL ExtF] Intensity ExtF_Width= 0.000000 fs # [NL ExtF] Field Width ExtF_kind= "DELTA" # [NL ExtF] Kind(SIN|SOFTSIN|RES|ANTIRES|GAUSS|DELTA|QSSIN) ExtF_Tstart= 0.0100 fs # [NL ExtF] Initial Time % GfnQP_E 3.000000 | 1.000000 | 1.000000 | # [EXTQP G] E parameters (c/v) eV|adim|adim %Notice that we introduced a scissor operator (a rigid shif of the conduction bands) of 3.0 eV. In principle it is possible to perform a G

This tutorial will show how to perform a simple real-time BSE calculation with lumen on hBN monolayer. DFT inputs are available here: QE_inputs or ABINIT_inputs.

Follow the same steps of the linear-response tutorial, but when you generate the lumen input file use:

nlinear # [R NL] Non-linear optics em1s # [R Xs] Static Inverse Dielectric Matrix Chimod= "hartree" # [X] IP/Hartree/ALDA/LRC/BSfxc % BndsRnXs 1 | 20 | # [Xs] Polarization function bands % NGsBlkXs= 5 RL # [Xs] Response block size % DmRngeXs 0.10000 | 0.10000 | eV # [Xs] Damping range % % LongDrXs 0.000 |0.1000E-4 | 0.000 | # [Xs] [cc] Electric Field % % NLBands 4 | 5 | # [NL] Bands % NLstep= 0.0100 fs # [NL] Real Time step length NLtime= 55.00000 fs # [NL] Simulation Time NLverbosity= "high" # [NL] Verbosity level (low | high) NLintegrator= "CRANKNIC" # [NL] Integrator ("EULEREXP/RK4/RK2EXP/HEUN/INVINT/CRANKNIC") NLCorrelation= "SEX" # [NL] Correlation ("IPA/HARTREE/TDDFT/LRC/JGM/SEX/HF") NLLrcAlpha= 0.000000 # [NL] Long Range Correction % NLEnRange 0.200000 | 8.000000 | eV # [NL] Energy range % NLEnSteps= 1 # [NL] Energy steps NLDamping= 0.10000 eV # [NL] Damping NLGvecs= 107 RL # [NL] Number of G vectors in NL dynamics for Hartree/TDDFT % ExtF_Dir 0.000000 | 1.000000 | 0.000000 | # [NL ExtF] Versor % ExtF_kind= "DELTA" # [NL ExtF] Kind(SIN|SOFTSIN|RES|ANTIRES|GAUSS|DELTA|QSSIN) GfnQPdb= "none" # [EXTQP G] Database GfnQP_N= 1 # [EXTQP G] Interpolation neighbours % GfnQP_E 3.000000 | 1.000000 | 1.000000 | # [EXTQP G] E parameters (c/v) eV|adim|adim %Notice that in the calculation we decreased the number of g-vectors in the Hartree term,

Now you can analyze the response with ypp as it was done the linear response tutorial and compare with the standard Bethe-Salpeter (input here):

You can use the SEX approximation for non-linear response too.