ITS 2004 Summer Visiting Fellows Program

August 10, 2004 - ITS Mini-symposia at Notre Dame

As part of the 2004 Summer Visiting Fellows Program, ITS welcomed four seminar speaker's on the University of Notre Dame campus: Prof. Ioan Kosztin from the University of Missouri-Columbia, Prof. Thorsten Ritz from the University of California-Irvine, Deyu Lu and Yan Li from the University of Illionois at Urbana-Champaign. They are members of a research team specially assembled for the Theoretical Modelling of Transport Properties of Membrane Channel Proteins and Carbon Nanotubes project which was awarded the Visiting Fellows grant by the Institute. The mini-symposia drew a large crowd of Notre Dame faculty and graduate students interested in the topics.

INSTITUTE FOR THEORETICAL SCIENCES (ITS) SEMINARS:

Molecular and Ionic Transport Through Channel Proteins and Carbon Nanotubes
Prof. Ioan Kosztin ~ University of Missouri - Columbia
Abstract: Membrane proteins play a crucial role in matter, energy and information exchange processes involving living cells. Recent developments in molecular modeling methods, in computational hardware and software, combined with the availability of high resolution crystal structure of a continuously growing number of membrane proteins, offer unprecedented opportunities in investigating at atomic resolution the underlying physical mechanism of molecular transport and selectivity of channel proteins. At the same time, this effort can be facilitated by a comparative study of molecular and ionic transport through, the structurally more simple, carbon nanotubes. A brief account of recent results and ongoing efforts in describing the transport of water, small molecules and ions through aquaporin channel proteins and single-walled carbon nanotubes will be presented.

Modern Theoretical Approaches to Modeling Biomolecules and Biomaterials
Prof. Thorsten Ritz ~ University of California - Irvine
Abstract: The increase in computational power coupled with recent conceptual advances allows theoretical and computational biophysics to predict rather than describe the function of biomolecular or biomimetic systems on the basis of molecular-level information. We will present several brief case studies exemplary for this approach, in particular quantum modeling of energy transfer to elucidate design principles in photosynthetic systems and the development of a successful test to identify the biophysical mechanism underlying the magnetic compass of migratory birds.

Induced Band Gap of Armchair Carbon Nanotubes by Symmetry Breaking
Yan Li ~ Beckman Institute, University of Illinois at Urbana-Champaign
Abstract: Armchair carbon nanotubes are metallic with two sub bands crossing at the Fermi level. By applying perturbations with angular dependence, it is possible to modify the electronic band structure and generate a band gap. We study the effect on the band structure of different angular modes $V_q\sim \cos q \theta$ within a tight-binding scheme. Using symmetry arguments, we demonstrate a band gap opening in these metallic nanotubes when certain selection rules are satisfied for both potential and nanotube structure. We estimate band gap opening as a function of both the external potential and the tube radius and suggest an effective mechanism of metal-semiconductor transition by combination of different forms of perturbations.

Electronic Structure and Dielectric Behavior of Finite-length Single-walled Armchair Carbon Nanotubes
Deyu Lu ~ Beckman Institute, University of Illinois at Urbana-Champaign
Abstract: The electronic structure and dielectric screening of finite-length armchair carbon nanotubes are studied within a tight-binding model, which well captures the oscillation pattern of the band gap as the tube length increases. We find that: (1) the parallel screening constant grows almost linearly with the length and shows little dependence on the band gap; (2) the perpendicular screening is strongly related to the band gap and converges to its bulk value when the length exceeds tens of radius. Our approach is employed to study the polarization effect of a short (6,6) nanotube in a wet environment, when water is inside the tube. This situation is of interest for biomimetic uses of carbon nanotubes. Incorporating this method into classic molecular dynamics simulations will help us to understand the molecular transport dynamics through carbon nanotubes.