Stability of Subnanometer MoS Wires under a Realistic Environment.

The interaction of small molecules with low-dimensional structures plays a major role in many important practical processes such as metal hydride formation, energy storage systems, and catalysis. In this work, we carried out first-principles density functional theory calculations of hydrogen and oxygen adsorption as well as their diffusion on subnanometer MoS nanowires. The nanowires are robust against adsorption of hydrogen. On the other hand, interaction with oxygen shows that the nanowires can oxidize with a small barrier (0.20 eV). In addition, our findings indicate that the interaction with hydrogen or oxygen does not modify the metallic character of the nanowire. The calculations also show that the singlet state is the most stable for 2O adsorbed on the MoS nanowire. Such results open the path for understanding the behavior of MoS nanowires under a realistic environment.

Electronic structure of molecular hydrogen in MoS2nanopores.

Atom controlled sub-nanometer MoS2pores have been recently fabricated with promising applications, such gas sensing, hydrogen storage and DNA translocation. In this work we carried out first-principles calculations of hydrogen adsorption in tiny MoS2nanopores. Some of the pores show metallic behaviour whereas others have a sizeable band gap. Whereas adsorption of molecular hydrogen on bare pores are dominated by physisorption, adsorption in the nanopores show chemisorption behaviour with high selectivity depending on the pore inner termination. Finally, we show that functionalization with copper atoms leads to does not improve dignificantly the adsorption energies of selected pores.

An adaptive design approach for defects distribution modeling in materials from first-principle calculations.

Designing and understanding the mechanism of non-stoichiometric materials with enhanced properties is challenging, both experimentally and even computationally, due to the large number of chemical spaces and their distributions through the material. In the current work, it is proposed a Machine Learning approach coupled with the Efficient Global Optimization (EGO) method-an Adaptive Design (AD)-to model local defects in materials from first-principle calculations. Our method takes into account the smallest sample set as possible, envisioning the material defect structure relationship with target properties for new insights. As an example, the AD framework allows us to study the stability and the structure of the modified goethite (Fe0.875Al0.125OOH) by considering a proper defect distribution, from first-principle calculations. The chemical space search for the modified goethite was evaluated by starting from different sizes and configurations of the samples as well as different surrogate models (ANN and Gaussian Process; GP), acquisition functions, and descriptors. Our results show that the same local solution of several defect arrangements in Fe0.875Al0.125OOH is found regardless of the initial sample and regression model. This indicates the efficiency of our search method. We also discuss the role of the descriptors in the accelerated global search for defects in material modeling. We conclude that the AD method applied in material defects is a successful approach in automating the search within huge chemical spaces from first-principle calculations by considering small samples. This method can be applied to mechanistic elucidation of non-stoichiometric materials, solid solutions, alloys, and Schottky and Frenkel defects, essential for material design and discovery. Graphical abstract.

Intense intrashell luminescence of Eu-doped single ZnO nanowires at room temperature by implantation created Eu-Oi complexes.

Successful doping and excellent optical activation of Eu(3+) ions in ZnO nanowires were achieved by ion implantation. We identified and assigned the origin of the intra-4f luminescence of Eu(3+) ions in ZnO by first-principles calculations to Eu-Oi complexes, which are formed during the nonequilibrium ion implantation process and subsequent annealing at 700 °C in air. Our targeted defect engineering resulted in intense intrashell luminescence of single ZnO:Eu nanowires dominating the photoluminescence spectrum even at room temperature. The high intensity enabled us to study the luminescence of single ZnO nanowires in detail, their behavior as a function of excitation power, waveguiding properties, and the decay time of the transition.

Toward an Accurate Density-Functional Tight-Binding Description of Zinc-Containing Compounds.

An extended self-consistent charge density-functional tight-binding (SCC-DFTB) parametrization for Zn-X (X = H, C, N, O, S, and Zn) interactions has been derived. The performance of this new parametrization has been validated by calculating the structural and energetic properties of zinc solid phases such as bulk Zn, ZnO, and ZnS; ZnO surfaces and nanostructures; adsorption of small species (H, CO2, and NH3) on ZnO surfaces; and zinc-containing complexes mimicking the biological environment. Our results show that the derived parameters are universal and fully transferable, describing all the above-mentioned systems with accuracies comparable to those of first-principles DFT results.