T. Thonhauser on Describing van der Waals Interactions in a Quantum-Mechanical Way
Fast Moving Front Commentary, July 2011
Article: Van der Waals density functional: Self-consistent potential and the nature of the van der Waals bond
Authors: Thonhauser, T;Cooper, VR;Li,
S;Puzder, A;Hyldgaard, P;Langreth, DC
T. Thonhauser talks with ScienceWatch.com and answers a few questions about this month's Fast Moving Fronts paper in the field of Physics.
Why do you think your paper is highly cited?
Simply said, we have provided a missing link with this paper that—at the time—the scientific community was waiting for. This paper introduces a theoretical formalism to describe weak interactions in materials (so-called van der Waals interactions) in a convenient quantum-mechanical way. The scientific community is currently trying to study many materials where these van der Waals interactions are important and that is why the paper has been so well received.
A wealth of applications, reaching from biological molecules to hydrogen-storage materials, that have been out of reach before can now be studied theoretically with high accuracy. Such theoretical studies have advantages over experimental studies in that we can study not-yet-existing materials, and it is also faster and more economical to scan a range of possible materials for different uses than to synthesize them in the lab. However, it is the combination of experiment and theory that provides the most powerful approaches for materials science today.
Does it describe a new discovery, methodology, or synthesis of knowledge?
In this paper we are extending and improving a previous methodology. The paper was built on an earlier developed formalism by some of the authors. More specifically, the groundwork for this paper was laid by Prof. David Langreth—who just recently passed away and who really should receive all credit for this excellent work. In the present paper, we extend this framework and make it self-consistent, which makes it very practical for implementations in the computer codes that are being used to model materials.
Would you summarize the significance of your paper in layman's terms?
"In the future, through this work and with growing computer power, it is conceivable that we will also study much larger systems, such as proteins, which will then have an even more direct impact on understanding diseases, creating cures thereof, and many other things."
This paper is significant because it provides a theoretical method to describe weak van der Waals interactions in materials in a convenient, accurate, practical, and simple-to-implement way. It is not that these van der Waals interactions could not have been described in the past; in fact, quantum chemistry and other methods are very successful in doing so, but they are either empirical or their calculation is numerically very expensive. The original work of Prof. Langreth reformulated the problem in a numerically inexpensive method, which we then together improved and completed in the present paper.
Let me give some examples of the types of materials we have recently been studying: Our research group is using this method to study such problems as the helical twist in DNA, the intercalation of anti-cancer drugs into DNA, and the storage of hydrogen in several materials for onboard solutions in vehicles.
How did you become involved in this research, and how would you describe the particular challenges, setbacks, and successes that you've encountered along the way?
It was Prof. Langreth who first interested me in this topic, now over five years ago. The first difficulty was to derive the corresponding framework mathematically. This was not necessarily very complicated, but rather tedious. The next difficulty, which was in fact a much larger one, was to translate the formalism and develop a numerically stable, fast, and efficient computer code. In this respect, we were relatively lucky in that fairly early on we had a functioning prototype for the code, with which we were then able to cross-check our mathematical derivation. The final challenge was then to find appropriate applications that showed the predictive power of our new approach.
Where do you see your research leading in the future?
At this point, the van der Waals interactions have been implemented into very many of the available standard computer codes for materials studies. As such, the larger scientific community is now moving to apply this framework to many interesting materials. In the near future, I expect to see new papers describing research on a wealth of materials.
As I mentioned above, my research group is currently focused on using this method in several different studies that we will continue in the future. For example, we are teaming up with a local experimentalist to study and design new anticancer drugs. In addition, we are working with another team of experimentalists to model and make a new material that holds hydrogen for use in vehicles.
Overall, the materials that can be modeled using this approach are virtually unlimited and many other research groups around the world are using this method to model other materials of current interest. I also hope to further develop the method to be able to describe other materials that are not accurately captured at this point.
Do you foresee any social or political implications for your research?
Currently, we are studying relatively small systems—for example, systems consisting of up to several hundred atoms. As such, most of the impact is limited to the materials science community. Much of our research is in very early stages and at fundamental levels. However, we are laying a foundation for better treatments to diseases such as cancer and the possibility of someday creating a hydrogen economy, replacing petrol-based fuels.
In the future, through this work and with growing computer power, it is conceivable that we will also study much larger systems, such as proteins, which will then have an even more direct impact on understanding diseases, creating cures thereof, and many other things. So, in this respect, there are profound social and political implications for this research.
Prof. T. Thonhauser
Department of Physics
Wake Forest University
Winston-Salem, NC, USA
KEYWORDS: VAN DER WAALS DENSITY FUNCTIONAL, SELF-CONSISTENT POTENTIAL, VAN DER WAALS BOND, GENERALIZED GRADIENT APPROXIMATION, INHOMOGENEOUS ELECTRON GAS, CORRELATION ENERGY, PERTERBATION THEORY, EXCHANGE, ACCURATE, SYSTEMS, MOLECULES, COMPLEXES, STACKING.