The physics in the Warm Dense Matter region of phase space is, by definition, not dominated by one single type of physical process. Instead many different processes compete and create a complicated multi-phase phase-space structure. We can usually describe each individual phase, dominated by one type of physics, by effective Hamiltonians and quasi-particle/perturbation theories (defined in a general sense). However, in order to make predictive calculations in the Warm Dense Matter region, it is imperative to start from the laws of nature, the Dirac Equation (Dirac), or its non-relativistic limit, the Schrödinger Equation (SE).
While extreme-scale computation has given us the ability to calculate properties of matter in the Warm Dense Matter region, computing power is not enough. Without a truly predictive set of equations supporting this capability, the computational approach will fail. My work is focused on improving the predictive capability of the underlying equations.
There are very accurate and predictive capabilities, based on the SE, in use in Quantum Chemistry calculations, such as the Coupled Cluster expansion. Even with extremely large super computers, however, the computational cost of these methodologies is prohibitive. This is an illustration of the constant competition between accuracy and computational cost in this field. Density Functional Theory (DFT), its time dependent implementation (TDDFT), and the even more efficient Orbital-Free approach (OFDFT), all have the needed formal theoretical foundation and, in addition, meet the mathematical requirements for supporting efficient computational approaches. However, presently available approximations for the exchange-correlation functional limit the predictive power of these approaches. In this talk, I will discuss my approach to designing new functionals, the subsystem functional approach, and my work on creating functionals for van der Waals' bonded systems, such as explosives, and materials containing elements with d- and f-electrons, such as actinides and transition metal systems. I will also touch upon how this approach can be used for creating kinetic energy functionals for OFDFT, the importance of including relativity for actinide systems, and the use of pseudo-potentials in Warm Dense Matter calculations.
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.