Pitching molecular fastballs through a hurricane

The first course I taught at Georgia Tech was a graduate course in statistical mechanics. I quickly discovered that a big barrier for my chemistry students was a lack of understanding of modern classical mechanics. Actually, this has also been a problem for them in learning quantum mechanics too. It might seem odd because classical mechanics is everywhere around you. It is simply the theory that describes the motion of baseballs, pool balls, and rockets. The details of the theory get amazingly complicated as you try to address interactions between the particles. Baseballs don't have such long range interactions so no worries there. But molecules do, and these interactions need to be included to understand the full complexity of molecules in classical (and quantum) mechanical regimes. In order to address this gap, I created a primer on classical mechanics that I have been sharing with my students ever since. But this document was not available to anyone beyond my classroom. So when I was asked to submit a review article on modern molecular dynamics, it was a no-brainier to include my primer at the front of the article so as to bring up readers up to speed on the classical equations of motion beyond Newton's day.

We didn't stop there, of course. The advanced review article, written with my collaborator, Dr. Alex Popov, also describes modern theoretical and computational methods for describing the motion of molecules in extreme environments far from equilibrium (like, for example, a hurricane). There are lots of ways in which this problem involves many moving parts (that is, many variables or degrees of freedom.). One of these involves the approximate separation in the characteristic scales of electrons and nuclei for which the 2013 Nobel Prize in Chemistry was, in part, awarded. Another involves the three-dimensional variables required to describe each atom in every molecule for which there usually are many. Think moles not scores. This increasing complexity gives rise to feedback loops that can explode (just like bad feedback on a microphone-speaker set-up), collapse or do something in between depending on very subtle balances in the interactions. Slowly, but surely, the scientific community is beginning to understand how to address these complex multiscale systems far from equilibrium. In our recent article, we reviewed the current state of the art in this area in the hope that it can help us and others advance the field.

The article was written in collaboration with Alexander V. Popov. The title is "Molecular dynamics out of equilibrium: Mechanics and measurables" and our work was funded by the National Science Foundation. It was recently made available on-line in WIREs Comput. Mol. Sci. 10.1002/wcms.1190, "Early View" (2014), and should be published soon.