Excitons and charge transfer states

Our new paper was just accepted by the Journal of Chemical Theory and Computation. And it is actually already available as a just accepted manuscript (Link). What we are looking at is the analysis of excited states. If an excited state contains several configurations, it is not only tedious to analyze it but a lot of information may be missed by considering the configurations independently. The problem is in particular significant in the case of delocalized states. Here our procedure, which is based on the transition density matrix, can provide a well defined automatized measure for delocalization, which is also independent on the orbital resolution.

Another challenging case is to differentiate between (Frenkel) excitonic and charge resonance transitions. For example if you look at a symmetric dimer: Then you know that there have to be excitonic resonance states and charge resonance states. But because all the orbitals are delocalized, it is not trivial to differentiate between them (unless you use our analysis tools).

In summary, I am kind of proud of it ... :) And interestingly one of my first blog posts about quantum chemistry, which I have not really thought of in the meantime, was concerned with a part of this paper: a singular value decomposition of the transition density matrix yielding the natural transition orbitals. Apparently I had the same taste in things I consider interesting five years ago...

Minimal Running

Nature did not make our heels soft enough. This is why we need at least an inch of foam under them when we run. Most of us overpronate in a way that requires expensive complicated support in our shoes. People running without arch support and custom insoles almost have to be declared insane. We are destined as a species of couch potatoes and car drivers. If we want to move on our own two feet we'd better do it rarely, slowly and only with expensive customized equipment.

But is that true? Modern research suggests no. In fact there are strong indications that humans specifically evolved to be long distance runners. But how are we are supposed to do it if our heels are so hard? The answer is that we are not supposed to land on them. A midfoot or even forefoot strike allows us to use our arches to perfectly cushion our steps (if only we don't have to much arch or pronation support stopping this movement). Even more, our calfs and Achilles tendons do not only work as a cushion, they let us store elastic energy allowing us to virtually bounce around like we are on springs.

An undisputable feature of modern running shoes is that they let you run in an unphysiological way. The traditional viewpoint is that Nike improved Nature. Thanks to cushioned soles we can have a comfortable running style with large strides landing on our heels, which would be unthinkable without shoes. Maybe that is true for a some people. However, what I noticed is that especially with my Asics "battleship" shoes containing every kind of protection, cushoning and support possible I get cramps in the soles of my feet after the first few steps of running. And treating blisters (possibly filled with blood) has become a routine task to be carried out after almost every run. So far I thought this was my fault and distance running was just not my thing. Now that I read this book "Born to Run" I am starting to believe that it was not my fault after all. Maybe I just need a more physiological running shoe (no heel-toe differential, less cushioning, less support) and then maybe my feet can just work in the way they are intended to work. Do I have flat feet and problems with pronation or are those muscles just weakened because I always have so much support under them? The first two runs with my new New Balance Minimus Road shoes suggests that minimal shoes may be the solution for me. Let's see if it stays like that ...

In summary: if you are fine as you are or you are not interested in running, stay as you are. But if not, it may well be worth the time to do some more research (for example starting here).