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Thursday, April 03, 2014

Quantum Embedding with Symmetry Breaking and Restoration: A Quantum Chemistry Approach to Molecular and Materials Modelling

Gomberg Lecture
1640 Chemistry
4:00 PM - 5:30 PM

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Speaker:   Gustavo Scuseria, Rice University
Abstract:   Despite its enormous success for both molecules and solids, modern density functional theory (DFT) faces significant hurdles for improving its current accuracy. The way forward in DFT has been to add pieces of wavefunction theory to it. This all started when Hartree-Fock exchange was included in the successful hybrid functionals. In solid state, the HSE screened hybrid has brought predictions of band structure and density of states (even of difficult materials like metal oxides) to unprecedented levels of accuracy. Yet, when strong correlations and emerging collective phenomena are present (e.g., superconductivity), this all breaks down. During the last few years, our research group has embarked in a quest for designing a wave function based electronic structure methodology that would be applicable to both molecules and solids, especially in the presence of strong correlations. The aim is to achieve this goal with low (polynomial, not combinatorial) computational cost. This talk will discuss (mostly at the conceptual level) the different pieces that go into such model and present benchmark results along the way. The two major pieces of the model are: (1) symmetry breaking and restoration as an impurity solver; (2) density matrix quantum embedding to capture entanglement of a strongly correlated unit cell with a bath mimicking the rest of the system. While this task is far from being completed, I will report on several successful milestones that make us very optimistic about the future of this model. References: [1] Projected quasiparticle theory for molecular electronic structure, G. E. Scuseria, C. A. Jimenez-Hoyos, T. M. Henderson, J. K. Ellis, and K. Samanta, J. Chem. Phys. 135, 124108 (2011). [2] Projected Hartree-Fock theory, C. A. Jimenez-Hoyos, T. M. Henderson, and G. E. Scuseria, J. Chem. Phys. 136, 164109 (2012). [3] Multi-reference symmetry-projected variational approaches for ground and excited states of the one-dimensional Hubbard model, R. R. Rodríguez-Guzmán, C. A. Jiménez-Hoyos, R. Schutski, and G. E. Scuseria, Phys. Rev. B 87, 235129 (2013). [4] Density matrix embedding theory from broken symmetry mean fields, I. W. Bulik, G. E. Scuseria, and J. Dukelsky, Phys. Rev. B 89, 035140 (2014).