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Toward Computational Design of Functional Nanostructures

Noa Marom
Tulane University

May 3, 2016

Computational materials design offers tremendous potential for discovery and innovation. This powerful concept relies on computational exploration of the vast configuration space of materials structure and composition to identify promising candidates with desired properties for target applications. In fact, many applications do not rely on a single material but on the combination of several materials in a functional nano-structure. Examples for functional nano-structures include the dye-oxide interface, at which charge separation is achieved in dye-sensitized solar cells, and nanocatalysts based on clusters dispersed on a large surface area support. Therefore, we would like to design not just a material, but a functional nano-structure. This requires the combination of accurate electronic structure methods with efficient optimization algorithms.
The electronic properties and the resulting functionality of a nano-structure cannot be deduced directly from those of its isolated constituents. Rather, they emerge from a complex interplay of quantum mechanical interactions that depend on the local environment at the nano-scale. Describing these effects requires a fully quantum mechanical first principles approach. In the first part of the talk, many-body perturbation theory within the GW approximation, where G is the one-particle Green’s function and W is the screened Coulomb interaction, is used to elucidate the size effects in the energy level alignment at the interface between dye molecules and TiO2 clusters of increasing size.
In the second part of the talk, a new approach is presented for computational design of clusters using property-based genetic algorithms (GAs). These algorithms perform optimization by simulating an evolutionary process, whereby child structures are created by combining fragments (“mating”) of the fittest parent structures with respect to the target property. Property-based GAs tailored to search for low energy, high vertical electron affinity (VEA), and low vertical ionization potential (VIP) are applied to TiO2 clusters with up to 20 stoichiometric units. Analysis of the resulting structures reveals the structural features associated with a high VEA and a low VIP and explains the absence of the expected size trends.

In his talk, Peng Liu (Pitt), describes the challenges of applying quantum mechanics to organic chemistry in order to explain and predict the underlying mechanisms of organic reactions.
In his studies, he applies theoretical models to investigate the mechanisms and origins of reactivity and selectivity of synthetically useful transition-metal-catalyzed reactions. He also develops new models for the analysis of catalyst-substrate interactions for the generation of quantitative, chemically meaningful, and predictive results that can be translated to the concepts of experimental organic chemistry.

In his talk, Robert Griffiths (CMU) wonders "where was the photon?" in a nested Mach-Zehnder interferometer.

He walks us along the path taken by a wave passing through a beam splitter before reaching a detector with pedagogy and humor!

Liang Fu (MIT) talks about recent developments in the control of Majorana fermions using the charging energy in mesoscopic systems.

In his talk, he addresses the following questions: can one probe the topological properties of Majorana Fermions in the solid state, specifically their non-locality as two Majorana Fermions share a single state. Then, can one use those topological properties in the field of quantum computation.

He then proceeds to demonstrate the latest developments in the entangled ares of theoretical physics, quantum information, and quantum materials.

The PQI2016 Public Lecture was given by Prof. Michel Devoret of Yale University. In his talk entitled “The Quest for the Robust Quantum Bit”, Devoret presents the progress of his group towards the conservation of quantum information via the use of “CAT-states”, a wink and a nudge to Schrodinger’s cat in its superposition of alive and dead states.

He describes the outstanding research carried out in his lab and the future considerations of his newly founded company, Quantum Circuits, Inc., which are taking us one step closer to the advent of the ultimate super computer: the quantum computer.