MC 3116

work:+1 212-854-4231

pechukas@chem.columbia.edu

Research Summary

I study molecular dynamics, but to tell the truth I am interested more in the dynamics than in the molecules, and I care most about questions of principle. Here are some such questions

1. There are a lot of things that closed systems - systems isolated from their surroundings - cannot do; for one thing, they cannot change their total energy. Open systems, which can exchange energy with their surroundings, can do much more. Still, it has been thought for many years that the only transformations possible in a quantum-mechanical open system are "completely positive" transformations, which are quite restrictive. We now know that this is not so. Open systems are restricted to "completely positive" motion only if the contact with the surroundings is weak. What are the restrictions when contact is strong? Are there any?
2. The simplest example of an open system is a single molecule doing Brownian motion in a fluid. Here, contact with the fluid is manifest as friction on the molecule. The strong-contact limit of high friction is, in classical mechanics, associated with the name "Smoluchowski." What is the Smoluchowski limit of quantum mechanics?
3. The simplest model for chemical reaction dynamics in a fluid is Brownian motion along the reaction coordinate. Here is a hard Brownian motion problem: motion over an activation barrier whose height fluctuates in time. It is a model for many complex kinetic processes, such as ligand rebinding in heme proteins, where the barrier depends on the fluctuating protein conformation and stochastically "gated" diffusion-controlled reactions that succeed only if the gate is open when reactants reach it. What is the kinetic theory of fluctuating barrier processes?

Back to Top

Back to Top