Tuesday, October 5, 2010

The good, the bad, and the nasty

Just a few minutes ago I was preparing my lectures for my graduate mechanics class. As I often do, I was once again distracted, thumbing through the latter pages of the textbook - marveling at the simple beauty of physics. Even classical physics is rich with phenomena, yet it is unified by simple ideas from the calculus of variations. I yearn to savor the physics that lies before me, but awaken to reality with every ping alerting me to a new email. Sadly, life is filled with trivial tasks that keep me from my passions.

The last few days brought some good and bad news. As I had anticipated, Nathans' revised manuscript was accepted for publication. And, Shoresh's and Mark's JOSA B paper, which I had previously reported as being highlighted on the Optical Society of America's website, was the second most downloaded JOSA B paper in September 2010. See http://www.opticsinfobase.org/josab/abstract.cfm?uri=josab-27-9-1849 for a free download of the paper.

The paper that I had submitted to the Journal of Chemical Computation and Theory with David Watkins, over which I waged a full out battle with the referees, was finally rejected. I had expected this outcome from the outset, but thought it worth a try. My intention was to expose a new audience to our work, but apparently, this was not to be. Below is the strongest criticism of our paper.

"Professor Kuzyk seems strongly taken with his own work but is not sufficiently mindful of the work by others. Perhaps the most egregious example deals with the issue of neglecting the effect of vibronic interactions on the static first hyperpolarizability. As justification he cites two of his own papers, but totally misses the extensive literature in this field showing that the vibronic effect cannot be ignored. There are, in fact, many instances where the vibronic term is comparable to, or larger than, the pure electronic contribution. Hence, the maximum value he uses (derived only by considering electrons) could easily be breached without invoking any exotic systems."

The reviewer is referring to the fact that I cited one of our papers that shows that vibronic states do not contribute substantially to the hyperpolarizability. Undoubtedly, in heated debates, the parties involved often speak past each other. To do my part, I am once again plowing through this literature to understand the issue. However, I find it is a bit annoying that the reviewer did not point out an error in our logic, but rather made sweeping statements. My guess is that it is certainly possible for real molecules to have vibronic contributions that are large compared with electronic excitations; but, I believe that when a quantum system is designed to have a hyperpolarizability near the fundamental limit, the vibronic contribution will never be as large. And since we are always concerned with the physics of a system near the limits, I believe that we are correct.

It is interesting that the reviewer states that the limit could easily be breached in the presence of vibronic states. Since the best molecules ever measured fall a factor of 30 short of the limit, I do not believe that the reviewer's confidence is justified.

Though this exchange with the reviewer was one of the nastier ones I have experienced, I find it all to be trivial in the larger scheme of things. Happiness is most abundant when I am absorbed in Physics. At some point, I will rewrite this manuscript, taking into account these comments, and will see how our results mesh with the body of scientific understanding. I take solace in the fact that people are reading our papers. I see this review not as a devastating blow, but as an opportunity for new investigations. The last 6 years of my research on fundamental limits were ignited by a comment that was published on my 2000 PRL paper. In the process of accumulating evidence to show the criticisms wrong, I made many discoveries and gained deep insights. These kinds of experiences should not be seen as defeat, but as an invigorating start to a new chapter of research.


  1. That's a really frustrating comment. Can you write a Hamiltonian that accounts for vibration? And does that Hamiltonian obey the sum rules?

  2. Actually, that is in essence what we did in our paper, which the reviewer dismisses without comment. One of my colleges who is an export in vibronic states sums up the state of affairs as follows:

    "Chernyak, Tretiak, and Mukamel show theoretically that vibrations make only a small contribution to the second-order hyperpolarizability, contrary to numerous papers of Kirtman and Bishop. Bishop, Champagne, and Kirtman, in their rebuttal, claim Mukamel is wrong in general but that he IS right for second- and third-harmonic generation."

    I think these issues are complex and do deserve more thought; but, the reviewer did no one a service by resorting to an argumentum ad hominem tactic without specifically addressing the point that was objectionable.