Sn3C2monolayer with transition metal adatom for gas sensing: a density functional theory studies.

The gas sensing properties of pristine Sn3C2monolayer and different transition metal adatom (TM-Sn3C2, where TM = Fe, Co, Ni, Cu, Ru, Rh, Pd and Ag) was investigated using van der Waals corrected density functional theory. The understanding and potential of use of Sn3C2monolayers as sensors or adsorbent for CO, CO2, NO, NO2and SO2gaseous molecules is evaluated by calculating the adsorption and desorption energetics. From the calculated adsorption energies, we found that the pristine Sn3C2monolayer and 3dTM has desirable properties for removal of the considered molecules based on their high adsorption energy, however the 4dTM is applicable as recoverable sensors. We applied an Arrhenius-type equation to evaluate the recovery time for the desorption of the molecules on the pristine and TM adatom on Sn3C2monolayer. We found that the negative adsorption energies from -1 to -2 eV of the molecules resulted in easier recovery of the adsorbed gases at reasonable temperatures compared to adsorption energies in between 0 and -1 eV (weakly physiosorbed) and below -2 eV (strongly chemisorbed). Hence, we obtained that the Rh-Sn3C2, Ru-Sn3C2, Pd-Sn3C2, Pd-Sn3C2, and Rh-Sn3C2monolayers are good recoverable scavengers for the CO, CO2, NO, NO2, and SO2molecules. The current theoretical calculations provide new insight on the effect of TM adatoms on the structural, electronic, and magnetic properties of the Sn3C2monolayer and different transition metal adatom as well as shed light on their application as gas sensors/scavengers.

N-doped direction-dependent electronic and mechanical properties of single-walled carbon nanotube (SWCNT) from a first-principles density functional theory (DFT) and MD-simulation.

In this paper, the electronic and mechanical properties of Nitrogen (N) doped (6,1) single walled carbon nanotube (SWCNT) is analysed based on the first principles density functional theory (DFT) and Molecular dynamic (MD) calculation. A systematic N-doping on SWCNT was performed along zigzag (zz) and armchair (ac) direction, where the armchair doping is parallel to tube axis while zigzag is along the cross-section perpendicular to tube axis. The zz and ac doping resulted in variations in the electronic properties of the even and odd number of N-dopant atoms. To evaluate the mechanical properties, ab - initio MD-simulations was carried out. We found a dependence of the tensile response of the tube on the dopant concentration and doping pattern. Single N-doped system show enhanced tensile stress by 55% as compared to the pristine SWCNT with marginal changes in the young's modulus for all N-doped systems.

Controlling the electronic and optical properties of HfS2 mono-layers via lanthanide substitutional doping: a DFT+U study.

Two dimensional HfS2 is a material with potential applications in the field of photo-catalysis and advanced solid state devices. Density functional theory with the Hubbard U parameter (DFT+U) calculations were carried out to investigate the structural, electronic and optical properties of lanthanide dopant atoms (LN = La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) in the HfS2 mono-layer. The calculated electronic band gap for a pristine HfS2 mono-layer is 1.30 eV with a non-magnetic ground state. The dopant substitutional energies under both Hf-rich and S-rich conditions were evaluated, with the S-rich condition for the dopant atoms being negative. This implies that the incorporation of these LN dopant atoms in the HfS2 is feasible and experimental realization possible. The introduction of LN dopant atoms in the HfS2 mono-layer resulted in a significant change of the material properties. We found that the presence of LN dopant atoms in the HfS2 mono-layer significantly alters its electronic ground states by introducing defect states as well as changes in the overall density of states profile resulting in a metallic ground state for the doped mono-layers. The doped mono-layers are all magnetic with the exception of La and Lu dopant atoms. We found that LN dopant atoms in the HfS2 mono-layer influence the absorption and reflectivity spectra with the introduction of states in the lower frequency range (<1.30 eV). Furthermore, we showed that the applicability of doped HfS2 mono-layers as photo-catalysts is very different compared with the pristine HfS2 mono-layer.

First principles LDA + U and GGA + U study of protactinium and protactinium oxides: dependence on the effective U parameter.

The electronic structure and properties of protactinium and its oxides (PaO and PaO2) have been studied within the framework of the local density approximation (LDA), the Perdew-Burke-Ernzerhof generalized gradient approximation [GGA(PBE)], LDA + U and GGA(PBE) + U implementations of density functional theory. The dependence of selected observables of these materials on the effective U parameter has been investigated in detail. The examined properties include lattice constants, bulk moduli, the effect of charge density distributions, the hybridization of the 5f orbital and the energy of formation for PaO and PaO2. The LDA gives better agreement with experiment for the bulk modulus than the GGA for Pa but the GGA gives better structural properties. We found that PaO is metallic and PaO2 is a Mott-Hubbard insulator. This is consistent with observations for the other actinide oxides. We discover that GGA and LDA incorrectly give metallic behavior for PaO2. The GGA(PBE) + U calculated indirect band gap of 3.48 eV reported for PaO2 is a prediction and should stimulate further studies of this material.