Floppy organic LEDs

In Telluride last week Peter Rossky gave a nice talk about work in his group on electronic properties and excited state dynamics of conjugated molecules such as PPV used in LEDs and Organic Photovoltaics. One thing he emphasized was that cartoon pictures of these molecules as rigid and planar are not accurate. At room temperature molecules such a PPV can flop around substantially, as described in this paper.

A sleepless seminar in Seattle

Next tuesday I am visiting the Chemistry Department at University of Washington. I am giving a seminar on "Charge distribution near oxygen vacancies in cerium oxides". It is based on Elvis Shoko's Ph.D thesis work, also done with Michael Smith. A nice summary is in a review article we just published. I will post a copy of the talk when it is ready, but it will be similar to a seminar that Elvis gave at the oral defense of his thesis.

At UW I am looking forward to meeting Charlie Campbell and Xiaosong Li. Unfortunately, Oleg Prezhdo will not be there because he is moving to Rochester.

Jumping from one surface to another

Many interesting chemical processes involve non-adiabatic processes, i.e., they involve transitions between different potential energy surfaces and thus a break-down of the Born-Oppenheimer approximation. Calculating the rate of such processes (even in "toy" models, let alone full electronic structure theory calculations) is a great challenge.

One of the most stimulating talks I heard last week in Telluride was by Joe Subotnik. He gave a nice review of this problem and the "Tully problems" used as a benchmark.

Strategies for treating the problem with increasing sophistication (and computational cost) are something like:

• Ehrenfest mean-field dynamics
• Surface hopping
• Ehrenfest + decoherence (Prezhdo, Rossky, Schwartz...)
• Semi-classical dynamics (Miller–Meyer–Stock–Thoss formalism)
• Partial Wigner transforms (Kapral)
• Multiple spawning
• Full nuclear quantum dynamics

A recent J. Chem. Phys. paper by Joe also gives a good overview. This is all stuff I need to get a better handle on ....

The next Einsteins?

This week I am on holidays (vacation) with my nieces in Portland, Oregon. Yesterday, we went to the Oregon Museum of Science and Industry (OMSI). By chance, they had a special visiting exhibit, Einstein: the world through his eyes. It included the medal and certificates for his Nobel Prize (shown above with my nieces) and the original hand-written manuscript for his 1917 paper on general relativity.

One thing I always find interesting is how little play his 1905 paper on Brownian motion gets. I agree that for theoretical physics this paper was not as important as the special relativity paper and photoelectric papers of 1905. However, it can be argued that for science I actually think this was the most important paper of the 4 from 1905. After all, this led to Perrin's Brownian motion experiments in 1909 which finally convinced people that atoms really did exist (and recognised in the 1926 Nobel Prize in Physics). Furthermore, the Einstein relation between the diffusion constant and viscosity was the first example of a fluctuation-dissipation relation.

A century after van der Waals Nobel Prize

The director of the UQ Physics Museum, Norm Heckenberg asked me to give a public lecture marking the centennial of the 1910 Nobel Prize in Physics.

Johannes van der Waals received the Prize in 1910 "for his work on the equation of state for gases and liquids". Reading his biography and prize speech (in preparation for the talk on August 17) increased my appreciation for just how significant van der Waals work was, both in itself and in terms of what it led to.

His significant achievements include:

1. realising that the gas and liquid are actually the same phase of matter and could be described by the same equation of state

2. the law of corresponding states

3. the Gibbs free energy is the fundamental quantity needed to understand transitions between different phases of matter

van der Waals contributions were not just significant in that they provided an explanation for existing experimental data on a diversity of gases but they also led to completely new and unexpected scientific insights and discoveries, including:

a. the law of corresponding states led to some of the most important concepts in theoretical physics today: universality, scaling, and the renormalisation group.

b. the law of corresponding states guided Kamerlingh Onnes to the liquification of hydrogen and helium. this led to the discovery of superconductivity and superfluidity.

c. van der Waals theory of binary mixtures highlighted that the Gibbs free energy is the key quantity for understanding phase transitions.

d. the hypothesis of the van der Waals force for non-polar molecules (a residual attractive interaction between neutral spherical and uncharged atoms such as helium and argon) was explained by Fritz London and Eisenschitz in 1930, following the development of quantum theory. Their use of the notion of interactions mediated by virtual transitions turned out to be a foundational idea in quantum field theory where low-energy interactions are determined by high-energy states and processes.

AC or DC?

Today in Telluride I had some free time and so I hiked up the valley towards Bridal Veil falls. It turns out this is a very historic location because it is the location of the worlds first commercial AC power plant. It was built by Westinghouse and Nikola Tesla. This led to "the war of currents" with General Electric Current (headed by Thomas Edison and J.P. Morgan) who were advocating DC power.

Lectures on chemical dynamics

At the 2009 Telluride School on Theoretical Chemistry John Tully (Yale) gave a series of lectures on Chemical Dynamics (both quantum and classical). The slides look very clear and helpful.