[Wien] Adding excitonic effects

[Xavier Rocquefelte]

To properly describe an exciton, which is a two-particle entitie, you need a two-particle theory at least. 
DFT is a one particle theory, thus it is not suited to properly describe excitonic effects. 
For solids you must use the Bethe Salpeter Equation (BSE) which is implemented in other codes and very expensive in terms of computational time and memory. Another strategy is to mimick the effect of the exciton on the optical properties using DFT and a corehole approach. This last strategy is pragmatic and not exact, but it allows to deals with this 2-particle problem using a one-particle approach in a mean-field manner. Usually, a half corehole is used. It corresponds to the Slater transition state and it gives nice results in general. What kind of transtions are your doing? Does it implies core states? If yes you can easily remove half an electron in the file case.inc. If the transition is from valence states, the problem is more tricky to solve. 
Best Regards
Xavier

Dileep Krishnan <dileep at jncasr.ac.in> a écrit :

> Hi Users and Developers,
>
> I was calculating optical properties by OPTIC program. How can I add 
> excitonic effects into the calculation?
>
> --
> Dileep Krishnan,
> Int. Ph. D Student,
> International Centre for Materials Science (ICMS),
> Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR),
> Jakkur, Bangalore-560064,
> INDIA.
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