How to calculate the exciton state density

[shan dong]

Dear all,
After we've calculated the exciton dispersion, I wonder is there any way to get the exciton state density ?

[Davide Sangalli]

Dear Shan Dong,
if you solve the BSE with the input variable

Code: Select all

BSEprop="abs jdos esrt"

you will get the excitonc dos for each q-point (it does not work with Haydock however, only with diago and slepc solvers).

After that, you would just need to sum the output of the jdos files.
Please remember to correctly weight each q-point according to its weight in the BZ.

Best,
D.

[shan dong]

Dear Shan Dong,
if you solve the BSE with the input variable

Code: Select all

BSEprop="abs jdos esrt"

you will get the excitonc dos for each q-point (it does not work with Haydock however, only with diago and slepc solvers).

After that, you would just need to sum the output of the jdos files.
Please remember to correctly weight each q-point according to its weight in the BZ.

Best,
D.

Dear Davide Sangalli,
The jdos characterizes the number of transitions between a certain energyrange Ec,k − Ev,k. But in the special case of excitonic insulators, where the excitation energy is less than zero, there are some exciton states, most of which are dark states. How can we describe the state density of this part of the exciton?

Thanks a lot for your support.

[Davide Sangalli]

With BSEprop="jdos" you will get, for every q, both:
- the IP-JODS, e.g. the number of transitions between a certain energyrange Ec,k − Ev,k-q
- the excitonic version, e-g. the excitonic JOS where the IP transitions are replaced by E_{\lambda,q}

Best,
D.

[shan dong]

With BSEprop="jdos" you will get, for every q, both:
- the IP-JODS, e.g. the number of transitions between a certain energyrange Ec,k − Ev,k-q
- the excitonic version, e-g. the excitonic JOS where the IP transitions are replaced by E_{\lambda,q}

Best,
D.

Dear Davide Sangalli,
Thank you very much for your timely reply. I still have some questions about the excitonic JDOS. What does the JDOS peak value mean? Does it represent the strength of the transition (proportional to the vibrator strength), or the number of transitions? (The higher the number of excitons, the higher the peak), if it represents the density of the number of excitons of the transition, do the excitons of these transitions contain dark excitons with very weak transition strengths?

[Daniele Varsano]

Dear Shan Dong,

In the definition of the Joint density of states or excitonic density of states, the strength of the exciton is irrelevant:

For the definitions, you can have a look at the Stefan Albrecht PhD these available here:
https://inis.iaea.org/collection/NCLCol ... 12.pdf?r=1

Pag. 36 Eq. 3.22- 3.23 IP-Joint density of states.

Pag. 101 Eq. 4.10 Excitonic density of states.

Best,

Daniele