WFU Physics Colloquium

TITLE: Advancing Electronic Structure Theory: From van der Waals to NMR

SPEAKER: Dr. Timo Thonhauser,

TIME: Tuesday Dec. 4, 2007 at 2:30 PM^***

PLACE: George P. Williams, Jr. Lecture Hall, (Olin 101)

^***Note unusual time.

In this talk I will discuss two aspects of my recent work in electronic-structure theory. First, I will address a shortcoming of standard density functional theory, which gives poor results for systems with van der Waals interactions such as many biomaterials and layered structures. To remedy the situation, I will introduce a new exchange-correlation functional that includes van der Waals interactions in a seamless manner. The main advantage of our approach is the much more favorable scaling of the computational expense compared to standard quantum-chemistry approaches. Second, I will present a Wannier-function approach to derive a fully quantum-mechanical theory for the orbital magnetization in periodic crystals. I will then outline a novel way to calculate NMR chemical shielding tensors based on this new theory: instead of obtaining the shielding tensor from the response to an external magnetic field, we derive it directly from the orbital magnetization appearing in response to a microscopic magnetic dipole. The advantage of our approach is that it is simple and straightforward to implement because all complexities concerning the choice of the gauge origin are avoided and the need for a linear-response implementation is circumvented. At the end of my talk I show how the combination of NMR and van der Waals DFT open interesting possibilities for future research in condensed matter physics and materials science. I will outline applications to currently outstanding problems in nano-, bio-, and energy-related materials.