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Mardi 21 janvier 2020 - 14:00

Beyond standard methods to solve the many-body problem

Bruno Senjean (Institut Lorentz, Université de Leyde)

par Revaz Ramazashvili - 21 janvier 2020

Strongly correlated materials (like transition metal oxides) have attracted much attention over the years and remain one of the most challenging research topics, gathering chemists and physicists, theoreticians and experimentalists. Being able to understand and even predict the properties of such systems can shape the technologies of the future by the design of new nanodevices, with applications to energy conversion and electronic transport for solar cells, or superconducting magnets generating strong magnetic fields, etc.

Unfortunately, this requires to solve the electronic structure problem which scales exponentially with the system size. Nowadays, workarounds to this exponential wall problem are the use of truncated wavefunction-based correlation methods (in chemistry), reduced quantities (density, density matrices, or Green’s function) or Monte Carlo techniques. Despite significant progress, no method has shown to rule over the others both in terms of computational cost and accuracy.

To tackle this challenge, I have worked on three different strategies to go beyond standard approaches :

1) Increasing the versatility of Kohn-Sham density functional theory (DFT), which is a ground-state method, by generalizing the theory to ensembles.

2) Merging wavefunction-based method and DFT in an in-principle exact embedding theory, free from double counting problem.

3) Using Quantum Computing which provides an exponential speed-up to solve the electronic structure problem.

I will dedicate 15 minutes for each of those formalisms, which all serve the same purpose : solving the many-body problem.

Post-scriptum :

contact : P. Romaniello