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Understanding nano-materials from the quantum perspective

Final Activity Report Summary - NANOQUANT (Understanding Nano-Materials From the Quantum Perspective)

The objectives of the NANOQUANT project referred to both basic science and applications. At the low end, the objective was to develop a conceptually and mathematically consistent rigorous electronic structure toolbox, applicable at the nanoscale and intended for accurate calculations of structures and properties and for predicting structure to property relationships. At the high end, the goal of the network was to act as an active modelling unit, providing theoretical support to experimental activities such as synthesis, materials characterisation and the ‘design of devices’.

The research was conducted within six interconnected areas:

1. nanoscale quantum modelling. An essential objective of the network was to transfer the scale of quantum modelling from the atomic domain into the nano domain. Indeed, without its fulfilment, we could not hope to reach the other objectives of understanding nanomaterials from a quantum perspective and modelling materials of technological interest. A primary target of the network was therefore to develop a linear-scaling technique, i.e. a technique with a cost proportional to the system size, which brought quantum modelling into the nano regime.
2. large-scale developments of high-level correlation methods. Because of its computational simplicity, the main thrust of the development of quantum methods towards the nanoscale regime took place within the realm of density functional theory (DFT). Nevertheless, it was essential that a similar development was also undertaken for the hierarchical ab initio methods. Work with coupled-cluster theory, the use of the so-called Cholesky decomposition, Laplace transforms, and resolution-of-identity, i.e. density-fitting, techniques was conducted within NANOQUANT.
3. multi-configurational relativistic DFT. Apart from extending the scale and scope of the applicability range of current electronic structure techniques into the nano domain, it remained important to study and develop the basic aspects of electronic structure theory itself. In particular, we focussed on the role of spin and spin states in open-shell systems and on four-component relativistic electronic-structure theory.
4. modelling of characterising techniques. We used the developed technology to model various magnetic resonance processes, such as nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR) and optically detected magnetic resonance (ODMR). We likewise pursued modelling of vibrational Raman optical activity (VROA) in the infrared region, natural and magnetically induced circular dichroism in the optical region and Raman scattering in the X-ray region.
5. molecular and nano-electronics. Since this was an important area for nano applications, the network focussed on non-equilibrium Green’s function theory to describe the potential distribution and current voltage characterisation of molecular or nano devices. A goal was to predict the optimal size and shape for metal contacts and molecular bridges of devices such as switches and transistors. The conductivity of nanotubes and biological molecules was also investigated.
6. molecular and nano-photonics. In the emergence of modern information society, the technology of photonics plays a pivotal role. In order to fully understand the functionality of various photonic devices such as conductors, wave guides, switches and displays, we considered it essential to master and simulate the basic photon-matter interaction. An additional task of the NANOQUANT network was to consolidate and extend the functionality of the existing fourth-order toolbox for electromagnetic properties to the nanoscale regime, involving the adaptation of density-matrix based response theory.

Through tight collaboration between the project partners, the NANOQUANT network was successful in fulfilling its scientific goals. It was also successful in training 30 young European researchers through a dense program including summer schools, conferences, visits, twinning and career exploration actions.