Adiabatic Connection and Virial Theorem for Ensemble Density Functional Theory

Ensemble density functional theory (DFT) establishes a natural framework for thermal DFT and provides excited state information inaccessible through other DFT methods. However, development of better exchange-correlation approximations is needed for this theory to be of practical use [1]. In this talk, the adiabatic connection [2] and virial theorem for ensemble DFT will be presented. In particular, their relation to exact ensemble DFT calculations, dependence on ensemble weights, and a new method for extracting exact ensemble exchange-correlation potentials will be explored. [1] Gidopoulos, N. I. and Papaconstantinou, P. G. and Gross, E. K. U. {\it Phys. Rev. Lett.}, {\bf 88}, 033003 (2002). [2] Nagy, A. {\it Int. J. Quant. Chem.}, {\bf 56}, 225 -- 228 (1995).