Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userBlack Arsenic as an Optimum Gas Sensor: vdW Corrected Density Functional Theory Calculations
117
0
0.0
(
0
)
Added by
Rameshwar L. Kumawat
Publication date
2020
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
Recent experiments demonstrate the synthesis of 2D black arsenic exhibits excellent electronic and transport properties for nanoscale device applications. Herein, we study by first principle calculations density functional theory together with non equilibrium Greens function methods, the structural, electronic, adsorption strength, charge transfer, and transport properties of five gas molecules CO, CO2, NO, NO2, and NH3 on a monolayer of black arsenic. Our findings suggest optimum sensing performance of black arsenic that can even surpass that of other 2D material such as graphene. Further, we note the optimum adsorption sites for all the five gas molecules on the black arsenic and significant charge transfer between the gas molecules and black arsenic are responsible for optimum adsorption strength. Particularly, the significant charger transfer is a sign that the interaction between the target gas molecule and nanoscale device is sufficient to yield noticeable changes in the electronic transport properties. As a proof of principle, we have examined the sensitivity of a modeled nano-scale device towards CO, CO2, NO, NO2, and NH3 gas molecules, indicating that it is indeed possible to reliably detect all the five gas molecules. Thus, based on all these findings, such as sensitivity and selectivity to all the five gas molecules adsorption make black arsenic a promising material as an optimum gas sensor nano-scale device.
rate research
Read More
Density Functional Theory calculations are used to investigate the role of substrate-induced cooperative effects on the adsorption of water on a partially oxidized transition metal surface, O(2x2)/Ru(0001). Focussing particularly on the dimer configuration, we analyze the different contributions to its binding energy. A significant reinforcement of the intermolecular hydrogen-bond (H-bond), also supported by the observed frequency shifts of the vibration modes, is attributed to the polarization of the donor molecule when bonded to the Ru atoms in the substrate. This result is further confirmed by our calculations for a water dimer interacting with a small Ru cluster, which clearly show that the observed effect does not depend critically on fine structural details and/or the presence of co-adsorbates. Interestingly, the cooperative reinforcement of the H-bond is suppressed when the acceptor molecule, instead of the donor, is bonded to the surface. This simple observation can be used to rationalize the relative stability of different condensed structures of water on metallic substrates.
We systematically calculate the structure, formation enthalpy, formation free energy, elastic constants and electronic structure of Ti$_{0.98}$X$_{0.02}$ system by density functional theory (DFT) simulations to explore the effect of transition metal X (X=Ag, Cd, Co, Cr, Cu, Fe, Mn, Mo, Nb, Ni, Pd, Rh, Ru, Tc, and Zn) on the stability mechanism of $beta$-titanium. Based on our calculations, the results of formation enthalpy and free energy show that adding trace X is beneficial to the thermodynamic stability of $beta$-titanium. This behavior is well explained by the density of state (DOS). However, the tetragonal shear moduli of Ti$_{0.98}$X$_{0.02}$ systems are negative, indicating that $beta$-titanium doping with a low concentration of X is still elastically unstable at 0 K. Therefore, we theoretically explain that $beta$-titanium doping with trace transition metal X is unstable in the ground state.
These lecture notes contain a brief practical introduction to doing density functional theory calculations for crystals using the open source Quantum Espresso software. The level is aimed at graduate students who are studying condensed matter or solid state physics, either theoretical or experimental.
Energy gaps are crucial aspects of the electronic structure of finite and extended systems. Whereas much is known about how to define and calculate charge gaps in density-functional theory (DFT), and about the relation between these gaps and derivative discontinuities of the exchange-correlation functional, much less is know about spin gaps. In this paper we give density-functional definitions of spin-conserving gaps, spin-flip gaps and the spin stiffness in terms of many-body energies and in terms of single-particle (Kohn-Sham) energies. Our definitions are as analogous as possible to those commonly made in the charge case, but important differences between spin and charge gaps emerge already on the single-particle level because unlike the fundamental charge gap spin gaps involve excited-state energies. Kohn-Sham and many-body spin gaps are predicted to differ, and the difference is related to derivative discontinuities that are similar to, but distinct from, those usually considered in the case of charge gaps. Both ensemble DFT and time-dependent DFT (TDDFT) can be used to calculate these spin discontinuities from a suitable functional. We illustrate our findings by evaluating our definitions for the Lithium atom, for which we calculate spin gaps and spin discontinuities by making use of near-exact Kohn-Sham eigenvalues and, independently, from the single-pole approximation to TDDFT. The many-body corrections to the Kohn-Sham spin gaps are found to be negative, i.e., single particle calculations tend to overestimate spin gaps while they underestimate charge gaps.
Standard flavors of density-functional theory (DFT) calculations are known to fail in describing anions, due to large self-interaction errors. The problem may be circumvented by using localized basis sets of reduced size, leaving no variational flexibility for the extra electron to delocalize. Alternatively, a recent approach exploiting DFT evaluations of total energies on electronic densities optimized at the Hartree-Fock (HF) level has been reported, showing that the self-interaction-free HF densities are able to lead to an improved description of the additional electron, returning affinities in close agreement with the experiments. Nonetheless, such an approach can fail when the HF densities are too inaccurate. Here, an alternative approach is presented, in which an embedding environment is used to stabilize the anion in a bound configuration. Similarly to the HF case, when computing total energies at the DFT level on these corrected densities, electron affinities in very good agreement with experiments can be recovered. The effect of the environment can be evaluated and removed by an extrapolation of the results to the limit of vanishing embedding. Moreover, the approach can be easily applied to DFT calculations with delocalized basis sets, e.g. plane-waves, for which alternative approaches are either not viable or more computationally demanding. The proposed extrapolation strategy can be thus applied also to extended systems, as often studied in condensed-matter physics and materials science, and we illustrate how the embedding environment can be exploited to determine the energy of an adsorbing anion - here a chloride ion on a metal surface - whose charge configuration would be incorrectly predicted by standard density functionals.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
