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Dynamical processes in open quantum systems: pushing the frontiers of theoretical spectroscopy

Final Report Summary - DYNAMO (Dynamical processes in open quantum systems: pushing the frontiers of theoretical spectroscopy)

The primary goal of the DYNamo project is to develop new concepts to build a novel theoretical framework for understanding, identifying, and quantifying different contributions to energy harvest and storage as well as describing transport mechanisms in natural light harvesting complexes, photovoltaic materials, fluorescent proteins and artificial (nanostructured) devices. The route to achieve this goal is twofold, through i) fundamental theoretical developments within time-dependent density functional theory (TDDFT) for the ab-initio description of open-quantum systems and quantum optimal control, and ii) to lay the foundations for a bottom-up approach to calculate and control the excited state dynamics of large molecular systems when they interact with their environment. We apply these developments to the following three scientific challenges: i) characterising matter out of equilibrium, ii) controlling material processes at the electronic level and tailoring material properties, and iii) mastering energy and information at the nanoscale.

The creation of a first-principles spatially and time-resolved multi-scale-spectroscopic modelling tool for arbitrary open quantum-systems in and out of equilibrium not only means meeting the challenges of clean energy solutions, but also many other old and new challenges in material science, chemistry, biomedicine, and nanotechnology, as well. The goal is to answer the following questions: What are the design principles of environment-assisted quantum transport in photosynthetic organisms that can be transferred to nano-structured materials such as organic photovoltaic materials? What are the fundamental limits of excitonic transport properties such as exciton diffusion lengths and recombination rates? Can those properties be controlled? What is the role of quantum coherence in the energy transport of photosynthetic complexes, photovoltaic materials and fluorescent proteins? What is the role of spatial confinement in water and proton transfer through porous membranes (nano-capillarity)?

During the second half of the project, we continued a detailed analysis of our newly developed density-functional formalism to handle light-matter interactions at all regimes from weak to ultra-strong coupling. We developed practical functionals for treating the quantum nature of photon-matter interactions based on the optimized effective potential as well as KLI approximations. The quality of those functionals has been tested for exact solvable models, and now we have to jump into more realistic systems. We completed the implementation of optimal control theory in a TDDFT framework to show spectroscopic control. This is the first step towards realizing a “control age in materials” in which the direction of electron movements with lasers can selectively trigger chemical reactions and processes and create new materials of relevance to our society. Another novel and important theoretical development that was achieved during this period is concerned with the description of non-adiabatic phenomena using conditional probabilities. This theory is very powerful, and the lowest order of the theory is already able to capture nuclear tunnelling and nuclear wave-packet splitting. On the more applied side, we focused on providing a microscopic understanding of the role of exciton dynamics, exciton-energy transfer and charge-transfer processes in organic-inorganic interfaces from applications in solar energy harvesting. We have identified/demonstrated i) novel steps in the quest for organic materials that are capable of converting solar energy into electricity, ii) terahertz modulation of UV light by graphene nanoribbons as well as light emission from defective BN nanotubes, iii) structural control of layered materials by infrared laser irradiation and strengthening weak cohesive forces among molecules and atoms by light, iv) unravelling of the intrinsic colour of chlorophyll and the use of gold oxidation to transform greenhouse gas into useful chemicals, and v) characterisation and synthesis of germanene: a novel two-dimensional germanium allotrope akin to graphene and silicene.
Concerning new methodologies, we have developed and implemented the following new tools in the freely distributed Octopus code (GNU-license): time-resolved pump-probe optical and electron spectroscopy for finite and extended systems including novel transparent boundary condition methods and time-dependent population analysis, quantum-optimal control, magneto-optical responses, ground-state complex resonance, Wannier interpolation schemes to deal with TD-hybrids and density-matrix based minimization approaches. More tools are continuously being developed and are freely distributed to the whole scientific community through Octopus. The number of independent Octopus developers has increased as a consequence of this ERC project. This development is very important for guaranteeing the long lifetime of the code and its high impact on the spectroscopic and materials science communities.