Electron Correlation from Vacuum Fluctuations

The traditional view of electron correlation is based on the cluster expansion of the correlation energy into contributions from pairs, triples,...of electrons. Fluctuation-based electronic structure methods, on the other hand, use vacuum fluctuations corresponding to virtual pairs of electrons and holes traveling forward and backward in time, and their multiples, to describe correlation in many-electron systems. The prototype fluctuation-based electronic structure method is the random phase approximation (RPA), which has evolved from a semi-analytical technique for model Hamiltonians to a powerful tool for ab initio electronic structure calculations in chemistry and materials science [1]. I will explain the key concepts underlying fluctuation-based electronic structure theory and highlight differences to traditional electronic structure methods. A link to many-body Green’s function theory is established through a recent variational generalized Kohn-Sham approach to RPA, which yields accurate quasiparticle energies [2]. Comparison with perturbative approaches for large weakly interacting systems illustrates the critical importance of Casimir-Polder size consistency[3], which is built into fluctuation-based electronic structure methods by design. Finally, I will explain how fluctuation-based electronic structure the recent discovery and characterization of new oxidation states of lanthanide and actinide elements with unconventional electronic structure such as Pu2+ [4], and discuss open questions and unresolved challenges.

Speaker: Filipp Furche, UC Irvine