Walsh Joyce (pocketgrape8)

Imaginary-time time-dependent Density functional theory (it-TDDFT) has been proposed as an alternative method for obtaining the ground state within density functional theory (DFT) which avoids some of the difficulties with convergence encountered by the self-consistent-field (SCF) iterative method. It-TDDFT was previously applied to clusters of atoms where it was demonstrated to converge in select cases where SCF had difficulty with convergence. In the present work we implement it-TDDFT propagation for \it periodic systems by modifying the Quantum ESPRESSO package, which uses a plane-wave basis with multiple $\boldsymbolk$ points, and has the options of non-collinear and DFT+U calculations using ultra-soft or norm-conserving pseudo potentials. We demonstrate that our implementation of it-TDDFT propagation with multiple $\boldsymbolk$ points is correct for DFT+U non-collinear calculations and for DFT+U calculations with ultra-soft pseudo potentials. Our implementation of it-TDDFT propagation converges to the exact SCF energy (up to the decimal guaranteed by double precision) in all but one case where it converged to a slightly lower value than SCF, suggesting a useful alternative for systems where SCF has difficulty reaching the Kohn-Sham ground state. In addition, we demonstrate that more rapid convergence can be achieved if we use adaptive-size imaginary-time-steps for different kinetic-energy plane-waves.Technological applications involving 2D MoS2 require transfer of CVD grown material from its original substrate and subsequent lithographic processes. Inevitably, those steps contaminate the surface of the 2D material with polymeric residues affecting the electronic and optical properties of the MoS2. Annealing in forming gas is considered an efficient treatment to partially remove such residues. However, hydrogen also interacts with MoS2 creating or saturating sulfur vacancies. Sulfur vacancies are known to be at the origin of n-doping evident in the majority of as-grown MoS2 samples. In this context, investigating the impact of thermal annealing in forming gas on the electronic and optical properties of MoS2 monolayer is technologically important. In order to address this topic, we have systematically studied the evolution of CVD grown MoS2 monolayer using Raman spectroscopy, photoluminescence, x-ray photoelectron spectroscopy and transport measurements through a series of thermal annealing in forming gas at temperatures up to 500 °C. Efficient removal of the polymeric residues is demonstrated at temperature as low as 200 °C. Above this value, carrier density modulation is identified by photoluminescence, x-ray photoelectron spectroscopy and electrical characterization and is correlated to the creation of sulfur vacancies. Finally, the degradation of the MoS2 single layer is verified with annealing at or above 350 °C through Raman and photocurrent measurements.We have systematically studied the structural, electrical transport, and magnetic properties of Gd0.1Ca0.9MnO3(GCMO) thin films in function of thickness, which ranged from 22 nm up to 220 nm. We found that, although no strong substrate-induced strain was detected for any thickness, a sudden change in the electric transport properties was observed when the film thickness increases above 80 nm. While thinner samples are insulating in the whole temperature range, the samples thicker than 80 nm show a clear insulator-to-metal (IMT) transition at around 100 K. The IMT coincides with the appearance of a ferromagnetic phase that is absent in the thinner samples. We associate this critical film thickness with a critical film thickness that induces a sudden change in domain configuration, from in-plane domain to a closed flux-type domains with out-of-plane orientations. These out-of-plane oriented domains are meta-stable ferromagnetic in nature and result in an IMT which is accompanied by a hysteretic magnetoresistance behavior.The ability of ionising radiation to induce ly