Dynamically amorphous character of electronic states in poly(dA)-poly(dT):
Will DNA make a good molecular wire?

James P. Lewis (Department of Physics and Astronomy, Brigham Young University, Provo, UT 84602-4658)

One very important inferface problem is in the area of molecular electronics. In creating devices, the problems of finding the appropriate way to attach molecules to electrodes must be overcome, and there are several issues to be addressed - 1) Does the molecule attach appropriately to the desired electrode without too much modification to the molecule, 2) does the attachment occur without destroying the molecules necessary charge transfer capabilities, and 3) does the desired molecule even give the desired properties? One area that we have explored is in DNA molecular electronics, or the possible use of DNA as a molecular wire.

The first atomistic density functional theory-based investigation of a large DNA strand (10 base pairs) was reported by J.P. Lewis et al. (1997). Since that work, considerable improvements to our ab initio local-orbital method (called FIREBALL) have been introduced. We will discuss some of these improvements in reference to our efforts to calculate large biomolecular systems, in particular DNA. In the literature, much experimental and theoretical work has been done in the area of trying to understand the electronic structure and electron (hole)-transfer properties of DNA. Experimental efforts indicate DNA conductivity covers all spectrum - an insulator, a semiconductor, a metal, and even local superconductivity.

However, due to the size of the problem, atomistic models with a quantum mechanical picture for large DNA strands containing several base pairs have made very little contribution in this area. One important avenue of investigation is the understanding of how the dynamics of the DNA strand might affect the electronic structure and hence the electron(hole)-transport. We will discuss results where state-of-the-art molecular dynamics simulations, including an explicit representation of solvent and counterions and a proper treatment of the long-ranged electrostatic interactions, of duplex DNA were performed. Snapshots of the trajectory were coupled to calculations of the electronic structure. Our results for a 'time-dependent' electronic structure of DNA will then be reported.