Tuesday 11 June 2019

Visualising electron correlation

How do you visualise the correlation between two particles? One option is to fix one of them at a specific region of space and look at the distribution of the other one. This is the principle behind a new method for visualising excitonic correlation just presented in a paper in ChemPhotoChem: Visualisation of Electronic Excited‐State Correlation in Real Space, and released within the TheoDORE 2.0 code. First, we have to interpret the excited state within the electron-hole picture as explained previously and compute the two-body electron-hole distribution. Then, we can fix one of the quasi-particles in space and observe the distribution of the other one.

Below, I am showing what this analysis looks like for a simple PPV oligomer. I am fixing the hole either at the terminal phenyl, the vinyl or the central phenyl and plot the corresponding electron distribution. In the case of the S1 state, the electron does not really care about the hole. The electron comfortably rests in the LUMO no matter what the hole does:

But for the S2 state things look completely differently. The electron now tries to actively avoid the hole as it moves through the system.
S3, for comparison, has a much more localised structure where the electron is always focussed on the centre.
S4 has a somewhat more complicated structure:

By the way, I realised that the same type of analysis has been recently performed for periodic computations as well. The difference is that in a periodic system every atom (or symmetry unit) will produce the same picture. In a finite system the picture also changes with the position of the probe.


Joaquin Barroso said...

Nice! Thanks for sharing. I think I'm gonna try this my self this very week with other molecules.

Felix said...

Yes, go for it! I hope the code is reasonably well documented. If something is unclear, you can use the discussion forum
or send me an email.

One comment: You will find something interesting only in the case of multiconfigurational states, or more precisely, the PR_NTO value has to be significantly above 1.