negative energy values in o.exc_I_sorted

[waynebeibei]

Dear all

I am trying to calculate the absorption spectrum of MoS2 using YAMBO. After a coarse BSE calculation test (the absorption spectrum is normal), I turn to get o.exc_I_sorted and o.exc_E_sorted using ‘ypp -e s’. However, as shown attached, the values of energy are negative. Any problem about it and how to fix it?

Many thanks...

Jiaxu Yan

[Daniele Varsano]

Dear Jiaxu Yan,
I can't see any problem with that. You are solving the BSE adding the coupling, i.w. the coupling
between the resonant part (transition valence--> conduction, positive energies) and anti-resonant part
(conduction --> valence, negative energies).
The solution of the total excitonic Hamiltonian will have the same number of positive energies and negative
energies. If the coupling is low, the negative energies should have the same modulus of the positive one
(have a look at o.exc_E_sorted). Of course what make sense in absorption are the excitation for E>0.

Best,

Daniele