exciton binding energy

[samaneh]

Hi Developers,
Would you please explain how we can estimate binding energy of exciton??
(Is it "bandgap - first exciton peak")
What is the difference between bright and dark exciton?
Best
S. Ataei, University of Tehran, Iran

[Daniele Varsano]

Dear Smanaeh,
Binding of an exciton: QP band gap - excitation energy of the exciton you are interested in.
Bright -> finite oscillator strength (intensity)
Dark --> zero or very small intensity (so no optically active).

Best,
Daniele

[samaneh]

Dear Daniele,
Thanks.
But if I want to compare exciton binding energy with PL peak
which excitation energy should be considered???
(Is it the first peak of imaginary part of the epsilon function??)
Best regards

[Daniele Varsano]

Dear Samaneh,
PL can be very hard to describe, it really depends on the physics of your system if comparing with the first excitation is a good approximation or not.
Anyway, you can discuss it with your colleagues and collaborators, this is not a question strictly related with the code.
Best,
Daniele

[samaneh]

Thanks a lot.
1- would you please explain what are the data in o.eel output file ???
2- There are a lot of data for constant dielectric function(w=0) in the output file(o.eps)
but according to the experimental data there is
just one value for it, how should we compare them??
Best regards

[Daniele Varsano]

1- would you please explain what are the data in o.eel output file ???

It is the eels spectrum (electron energy loss), essentially 1/eps_M(w).

2- There are a lot of data for constant dielectric function(w=0) in the output file(o.eps)
but according to the experimental data there is
just one value for it, how should we compare them??

As you can see in the top of the file you have:

Code: Select all

 E/ev[1]    eps /Im[2] eps /Re[3] eps0/Im[4] eps0/Re[5]

Energy, Im(eps(w)), Re(eps(w)), Im(eps0 (w)), Re(eps0(w)).
eps0 is the dielectric function calculated in the independent particle approximation.
So, this is not the static dielectric function, the static values is the one corresponding to E=0. The static dielectric constant is the real part.

All this info are explained in the tutorials.

Best,
Daniele

[samaneh]

Dear Daniele,
Cartesian coordinates in ypp.in for hole position is
a.u. or angstrom??
Best

[samaneh]

Dear daniele,
Does yambo -b mean the static dielectric with E=0???
Best

[Daniele Varsano]

Dear Smaneh,
simply typing yambo -H
you can see:

Code: Select all

-h		:Short Help
 -H		:Long Help
 -J <opt>	:Job string identifier
 -V <opt>	:Input file verbosity
		 [opt=RL,kpt,sc,qp,io,gen,resp,all]
 -F <opt>	:Input file
 -I <opt>	:Core I/O directory
 -O <opt>	:Additional I/O directory
 -C <opt>	:Communications I/O directory
 -N		:Skip MPI initialization
 -D		:DataBases properties
 -S		:DataBases fragmentation
 -M		:Memory distribution (parallel runs)
 -i		:Initialization
 -o <opt>	:Optics [opt=(c)hi is (G)-space / (b)se is (eh)-space ]
 -k <opt>	:Kernel [opt=hartree/alda/lrc/hf/sex]
		        (hf/sex only eh-space; lrc only G-space)
 -y <opt>	:BSE solver [opt=h/d/(p/f)i]
		        (h)aydock/(d)iagonalization/(i)nversion
 -c		:Coulomb interaction
 -x		:Hartree-Fock Self-energy and local XC
 -d		:Dynamical Inverse Dielectric Matrix
 -b		:Static Inverse Dielectric Matrix
 -p <opt>	:GW approximations [opt=(p)PA/(c)HOSEX]
 -g <opt>	:Dyson Equation solver
		 [opt=(n)ewton/(s)ecant/(g)reen]
 -l		:GoWo Quasiparticle lifetimes
 -a		:ACFDT Total Energy

it is the static inverse dielectric matrix (w=0!). It is the entire matrix epsm1_q(G,G') to be used in a BSE calculation and *not* the macroscopic dielectric constant. You do not have any output.

Daniele

[samaneh]

Thanks.
But how can I calculate the dielectric constant (E=0) with yambo code???