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In this paper, we report on numerical calculations of the spontaneous emission rates and Lamb shifts of a $^{87}\text{Rb}$ atom in a Rydberg-excited state $\left(n\leq30\right)$ located close to a silica optical nanofiber. We investigate how these quantities depend on the fiber's radius, the distance of the atom to the fiber, the direction of the atomic angular momentum polarization as well as the different atomic quantum numbers. We also study the contribution of quadrupolar transitions, which may be substantial for highly polarizable Rydberg states. Our calculations are performed in the macroscopic quantum electrodynamics formalism, based on the dyadic Green's function method. This allows us to take dispersive and absorptive characteristics of silica into account; this is of major importance since Rydberg atoms emit along many different transitions whose frequencies cover a wide range of the electromagnetic spectrum. Our work is an important initial step towards building a Rydberg atom-nanofiber interface for quantum optics and quantum information purposes.

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Purpose Technologies with low environmental impacts and promoting renewable energy sources are required to meet the energetic demand while facing the increase of gas emissions associated to the greenhouse effect and the depletion of fossil fuels. CO 2 methanation activated by magnetic heating has recently been reported as a highly efficient and innovative power-togas technology in a perspective of successful renewable energy storage and carbon dioxide valorisation. In this work, the life cycle assessment (LCA) of this process is performed, in order to highlight the environmental potential of the technology, and its competitivity with in respect to conventional heating technologies. Methods The IMPACT 2002+ was used for this LCA. The process studied integrates methanation, water electrolysis and CO 2 capture and separation. This "cradle-to-gate" LCA study does not consider the use of methane, which is the reaction product. The functional unit used is the energy content of the produced CH 4. The LCA was carried out using the energy mix data for the years 2020 and 2050 as given by the French Agency for Environment and Energy management (ADEME). Consumption data were either collected from literature or obtained from the LPCNO measurements as discussed by Marbaix (2019). The environmental impact of the CO 2 methanation activated by magnetic heating was compared with the environmental impact of a power-togas plant using conventional heating (Helmeth) and considering the environmental impact of the natural gas extraction. Results It is shown that the total flow rate of reactants, the source of CO 2 and the energy mix play a major role on the environmental impact of sustainable CH 4 production, whereas the lifetime of the considered catalyst has no significant influence. As a result of the possible improvements on the above-mentioned parameters, the whole process is expected to reduce by 75% in its environmental impact toward 2050. This illustrates the high environmental potential of the methanation activated by magnetic heating when coupled with industrial exhausts and renewable electricity production. Conclusions The technology is expected to be environmentally competitive compared with existing similar processes using external heating sources with the additional interest of being extremely dynamic in response, in line with the intermittency of renewable energy production.

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DIRAC is a freely distributed general-purpose program system for 1-, 2- and 4-component relativistic molecular calculations at the level of Hartree--Fock, Kohn--Sham (including range-separated theory), multiconfigurational self-consistent-field, multireference configuration interaction, coupled cluster and electron propagator theory. At the self-consistent-field level a highly original scheme, based on quaternion algebra, is implemented for the treatment of both spatial and time reversal symmetry. DIRAC features a very general module for the calculation of molecular properties that to a large extent may be defined by the user and further analyzed through a powerful visualization module. It allows the inclusion of environmental effects through three different classes of increasingly sophisticated embedding approaches: the implicit solvation polarizable continuum model, the explicit polarizable embedding, and frozen density embedding models. DIRAC was one of the earliest codes for relativistic molecular calculations and remains a reference in its field.

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Carbon nanotubes (CNTs), firstly synthesized in 1991, have shown great promise on a wide range of areas and are a current topic of research, both on a theoretical and experimental level. In this thesis, molecular properties of short CNTs as well as possible applications exploiting them as hosting systems were investigated by means of ab initio and molecular dynamics calculations. Single units of zigzag CNTs, namely cyclacenes, have been hypothesized more than 50 years ago. With the successful synthesis of CNTs, the interest in such systems and other types of carbon nanobelts has considerably increased, although their experimental realization has not been achieved yet. Therefore, predicting the molecular properties, the prospective applications and possibly providing important insight for the synthesis process based on theoretical approaches is of major interest. Notwithstanding, the challenges associated to cyclacenes are not only experimental, as previous theoretical works show controversial results about the electronic structure of this system. In this thesis, several electronic properties were derived analytically within the tight-binding approximation, providing asymptotic results at the thermodynamic limit for the total position spread tensor and the polarizability. The tight-binding trends were assessed by high level ab initio calculations, finding a good agreement between both methodologies. One major issue related to cyclacenes is the description of the electronic configuration of their ground state. By studying a wider range of system sizes, the polyradical character of the ground state was found to increase for increasing system size whereas the opposite trend was found for the singlet-triplet energy gap. Polynitrogen clusters have been suggested as environmentally friendly high energy-density material due to their particular bond energetics and their decomposition pathways into molecular nitrogen. However, their stability at ambient conditions is particularly poor, making their storage a major problem. An attempt to solve this challenge and stabilize polynitrogen systems is to confine them in nanomaterials. The encapsulation inside CNTs of different nitrogen clusters was studied by ab initio calculations.[...]

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