# What progress has been made in modelling photocatalytic reactions on semiconductor surfaces?

For example, are there any methods to allow for modeling of photo-oxidation or photo-reduction of a compound on a semiconductor surface? It appears there has been a lot of work on the bulk properties and recombination rate / exciton stability, but surface studies of these systems seem to be very problematic.

I suspect that this might just be outside of the region of computational studies I am familiar with so any insight into this type of study would be interesting to me.

• +1. Nice first question! We hope to see much more of you! By the way, were you aware of the gpaw tag? mattermodeling.stackexchange.com/questions/tagged/gpaw Jul 25 '20 at 20:03
• Yes, I work with gpaw and vasp somewhat regularly. I didn't see any reason to tag this as gpaw specific, but a photochemistry tag might be helpful in the future (but I am unable to make it). Jul 25 '20 at 20:07
• I was not suggesting to put the gpaw tag here, just wondering if you'd seen that we have several gpaw questions here already, in case you might be able to contribute to any of them (luckily they're all answered already, so maybe I'm just hoping you're aware of the tag for the future). Jul 25 '20 at 20:09
• That makes sense, I will likely be active in the mattermodeling community in general in the future. I think this is a very helpful SE site and will be doing my best to help others as well. I am glad to see that there are tags for individual calculators. Jul 25 '20 at 20:15
• Hi Tristan, too bad no one else answered the bounty. It would be sad to see the bounty go to waste, so Id appreciate if you could award it to me, although admittedly my answer is probably not exactly what you were looking for. Aug 3 '20 at 21:45

While I'm not familiar with surfaces, I can provide the theory for photoredox molecules. Presumably, this can be extended to surfaces with the correct level of theory, which perhaps others can elaborate on.

I'm quoting from reference 1 with some commentary in brackets

The reduction potentials associated with the excited states cannot be directly measured [but testing different compounds can give an upper bound] and are typically calculated from known cyclic voltammetry (CV) and spectroscopic data

As an approximation, the excited-state potentials of a catalyst are related to its ground state potentials and its zero−zero excitation energy (E0,0). E0,0 can be estimated by the difference in energy between *PC and PC which can be approximated by the maximum emission of the catalyst [or simulation].

Oxidative Quenching

$$E_{red}[PC^{+1}/PC^*] = E_{red}[PC^{+1}/PC] - E_{0,0}$$

$$\ce{PC^{+1} +e^{-1} -> PC^{*}}$$

Reductive Quenching

$$E_{red}[PC^*/PC^{-1}] = E_{red}[PC/PC^{-1}] + E_{0,0}$$

$$\ce{PC^{*} +e^{-1} -> PC^{-1}}$$

Reference

Shining Light on Photoredox Catalysis: Theory and Synthetic Applications Joseph W. Tucker and Corey R. J. Stephenson The Journal of Organic Chemistry 2012 77 (4), 1617-1622 DOI: 10.1021/jo202538x