First-principles Spin-polarized Density Functional Theory Research Articles

Prediction of the Half Metallicity in Ferromagnetic Germanium Telluride (GeTe) Doped with Titanium

This research work studies the structural, electronic and magnetic properties of Ge[Formula: see text]TixTe (for [Formula: see text], 0.50, 0.75, 1) compounds in rock-salt structure based on first-principles spin-polarized density functional theory. As it is implemented in WIEN2k code, the full-potential augmented plane-wave method was used in the investigation. To evaluate the structural properties of compounds, the exchange-correlation term is estimated using PBE-GGA approximation. For the other properties such as the electronic structures, densities of states and local moments, the generalized gradient approximation PBE-[Formula: see text] is used. The analysis of spin-polarized density of states has shown the half-metallic ferromagnetic character when [Formula: see text] and 0.75; while at [Formula: see text], we obtained near half-metallic behavior. In order to validate the effects resulting from exchange splitting process, we calculated the exchange constants [Formula: see text] and [Formula: see text]. For Ti atomics sites, the value of total magnetic moment has been estimated equal to [Formula: see text] in all studied compounds. We have found that the local magnetic moment of Ti is reduced and small local magnetic moments on nonmagnetic atomics sites of Ge and Te were created by the p-d hybridization effect.

Effects of Two Nearest V Substitution Doping on Magnetism of Monolayer CrSi2 via First-Principles Investigations

First-principles spin-polarized density functional theory (DFT) is employed to investigate the effect of two nearest V substitution doping on magnetism of two dimension (2D) monolayer CrSi2. Calculation of formation energy confirms that all V-doped monolayer CrSi2 are thermodynamically stable. A total density of states, near Fermi level, are derived mainly from 3d states of V atom. Additionally, calculated magnitudes of overlap populations and average transfer charge confirm that the chemical bonds are extremely weak covalent bands with strong ionic component. The total magnetic moment of the system reduces with V–V distances in the case of two V atoms doped monolayer CrSi2, indicating that the nearest-neighbor V atoms substitutions doping monolayer CrSi2 might be a promising candidate in future application of spintronics.

Magnetic Volume Effect of Hydrogen Diffusion in Palladium

The electronic and magnetic properties of palladium hydrogen are investigated using first-principles spin-polarized density functional theory. By studying the magnetic moments and electronic structures of hydrogen atoms diffusing in face-centered cubic structure of transition metal Pd, we found that the results of magnetic moments are exactly the same in the two direct octahedral interstitial site-octahedral interstitial site diffusion paths-i.e. the magnetic moments are the largest in the octahedral interstitial site, and the magnetic moments are the lowest in saddle point positions. We also studied on the density of states of some special points, with the result that the density of states near the Fermi level is mainly contributed by 4d electrons of Pd and the change of magnetic moments with the cell volume in the unit cell of transition metal Pd with a hydrogen atom.

The Effect of Functionalization on Spin-Polarized Transport of Gallium Nitride–Based Magnetic Tunnel Junctions

Using first-principles spin-polarized density functional theory computations, the effect of functionalization (fluorination and hydrogenation) on spin-polarized transport of gallium nitride (GaN) nanosheet–based magnetic tunnel junction (MTJ) with CrO2 as electrodes is investigated. The results show fluorinated GaN–based structure exhibits better spin filtration and high TMR (maximum ~ 99%), as compared with hydrogenated GaN (maximum TMR ~ 93%)– and pristine GaN (maximum TMR ~ 83%)–based structures. In addition, fluorinated GaN nanosheet exhibits a ferromagnetic behavior with a magnetic movement of 1.0 μb per fluorine atom. The magnetic movements for pristine GaN and hydrogenated GaN sheets are reported to be 0 μb and 0.9 μb per hydrogen atom, respectively. Higher TMR, better spin filtration, and ferromagnetic behavior for fluorinated GaN–based structure open up its possibility as spin filter (injector) in MTJs and other spin-based devices.

First-principles evaluation of electronic and optical properties of (Mo, C) codoped BaHfO3 for applications in photocatalysis

In this paper, we report first-principles spin-polarized density functional theory calculations for exploring the effect of aliovalent Mo and C dopants on the electronic properties and photocatalysis potential of doped modifications of wide-bandgap cubic perovskite oxide BaHfO3 for water splitting. The structural and thermodynamic properties are computed by using the generalized gradient approximation, whereas the modified Becke-Johnson local density approximation is used to calculate the electronic structures of pristine, cation (Mo), and anion (C) monodoped and cation-anion (Mo, C) codoped BaHfO3. The spin-polarized calculations reveal that substitutional dopants CO and MoHf in the BaHfO3 lattice are thermodynamically stable. The incorporation of C in the O site reduces the bandgap of BaHfO3 and acts as a double-acceptor system, whereas a metallic character is obtained when Mo is doped into the Hf site giving rise to a double-donor system. We show that the acceptor and donor states of the C- and Mo-monodoped BaHfO3 can be passivated by (Mo, C) codoping at nearest-neighbor Hf and O sites of the BaHfO3 lattice, respectively. Analysis of the calculated electronic structure and optical absorption of (Mo, C) codoped BaHfO3 with reference to the H2O oxidation and reduction potentials reveals that this system is a suitable candidate for efficient splitting of water through photocatalysis in the visible region of the electromagnetic spectrum.

Influence of chalcogen composition on the structural transition and on the electronic and optical properties of the monolayer titanium trichalcogenide ordered alloys.

Based on first-principles spin-polarized density functional theory, we investigate the effects of chalcogen composition on the structural, electronic, and optical properties of monolayer (where X and X' = S, Se, Te) ordered alloys with values of x of 0, 0.167, 0.333, 0.500, 0.667, 0.833, and 1. We determine the optimized geometry for all possible substitutional adsorptions of chalcogen atoms for each x composition, and identify the energetically most stable allotropes as a function of composition. Our extensive analysis reveals that the structural and electronic properties depend on the chemical composition of the monolayers, and the band gap of TiX3 nanosheets can be tuned by adjusting the ratio of chalcogen compositions. While substitutional doping of tellurium atoms into TiS3 or TiSe3 monolayers results in a semiconductor-metal transition, the alloys remain a semiconductor under the transition from TiS3 to TiSe3 with band gaps which are very suitable for optical devices and infrared detectors. We also find that each TiS3(1-x)Se3x structure has an anisotropic dielectric function. Because of the anisotropy of the dielectric function, they can be useful materials for application in the transition metal trichalcogenide-based nanoelectronics industry in the future.

Stability of single-layer and multilayer arsenene and their mechanical and electronic properties

Using first-principles spin-polarized density functional theory, we carried out an analysis on the atomic structure, stability, energetics, and mechanical and electronic properties of single-layer structures of arsenene. These are buckled honeycomb, symmetric, and asymmetric washboard arsenene structures. Our analysis is extended to include layered three-dimensional crystalline phase of arsenic, as well as bilayer and trilayer structures to reveal dimensionality effects. The buckled honeycomb and symmetric washboard structures are shown to maintain their stability at high temperatures even when they are freestanding. As a manifestation of the confinement effect, the large fundamental band gap of single-layer phases decreases with increasing number of layers and eventually is closed. Concomitantly, lattice constants partially increase, while interlayer distances decrease. The effects of hybrid functional or self-energy corrections together with the spin-orbit coupling on the electronic structure of arsenene are crucial. The responses of direct and indirect band gaps to biaxial or uniaxial strain are rather complex and directional; while the fundamental band gap decreases and changes from indirect to direct with the biaxial strain applied to buckled arsenene, these effects are strongly directional for washboard arsenene. The width and the indirect/direct character of the band gap can be tuned by the number of layers, as well as by applied uniaxial/biaxial strain.

Magnetic properties in BiFeO3 doped with Cu and Zn first-principles investigation

Based on first-principles spin-polarized density functional theory calculations, the electronic structures, and magnetic properties of Cu and Zn-doped BiFeO3 are investigated. The calculated formation energies show that Cu prefers to occupy Fe site, while the Zn prefer to occupy Bi site. All the doped BiFeO3 systems turn out to be favorable for G-type antiferromagnetic arrangement. The substitution of Cu and Zn for Fe produces a magnetic moment of 3.0 and 4.0 μB per dopant, respectively. The net magnetic moments are from the broken symmetry of the AFM spin ordering network. For the substitution of Cu and Zn for Bi, the net magnetic moment originates from Cu/Zn itself and hole introduced by Cu/Zn. Two-Cu/Zn-doped cases show various magnetic behaves. If O vacancy is far away from dopants, the O vacancies don't affect the net magnetic moment of the substitution of Cu and Zn for Fe, but have notable effect for Bi site doping. The O vacancies result in metallicity in all doped cases. Our study demonstrates that the nonmagnetic Cu and Zn doping will lead to the diversity and complexity of magnetic properties depending on doping sites, distance between dopants, intrinsic defect, and so on, which could be responsible for the observed various magnetic behaviors in Cu/Zn-doped BiFeO3 samples.

Catalytic reaction on FeN4/C site of nitrogen functionalized carbon nanotubes as cathode catalyst for hydrogen fuel cells

We utilized first-principles spin-polarized density functional theory (DFT) calculations to study the electrocatalytic reaction steps on FeN4/C site of carbon nanotubes. O2 molecule can be adsorbed and partially reduced on FeN4/C site without any activation energy barrier. The partially reduced O2 further reacts with H+ and e− through a direct pathway (DPW) and form two water molecules without any activation energy barrier. Through an indirect pathway (IDPW), there is an activation energy barrier of ~0.15eV for the formation of the first H2O molecule. The formation of the second H2O molecule through IDPW does not have any activation energy barrier.

Investigations of the half-metallic behavior and the magnetic and thermodynamic properties of half-Heusler CoMnTe and RuMnTe compounds: A first-principles study

First-principles spin-polarized density functional theory (DFT) investigations of the structural, electronic, magnetic, and thermodynamics characteristics of the half-Heusler, CoMnTe and RuMnTe compounds are carried out. Calculations are accomplished within a state of the art full-potential (FP) linearized (L) augmented plane wave plus a local orbital (APW + lo) computational approach framed within DFT. The generalized gradient approximation (GGA) parameterized by Perdew, Burke, and Ernzerhof (PBE) is implemented as an exchange correlation functional as a part of the total energy calculation. From the analysis of the calculated electronic band structure as well as the density of states for both compounds, a strong hybridization between d states of the higher valent transition metal (TM) atoms (Co, Ru) and lower valent TM atoms of (Mn) is observed. Furthermore, total and partial density of states (PDOS) of the ground state and the results of spin magnetic moments reveal that these compounds are both stable and ideal half-metallic ferromagnetic. The effects of the unit cell volume on the magnetic properties and half-metallicity are crucial. It is worth noting that our computed results of the total spin magnetic moments, for CoMnTe equal to 4 μB and 3 μB per unit cell for RuMnTe, nicely follow the rule μtot = Zt − 18. Using the quasi-harmonic Debye model, which considers the phononic effects, the effecs of pressure P and temperature T on the lattice parameter, bulk modulus, thermal expansion coefficient, Debye temperature, and heat capacity for these compounds are investigated for the first time.

Catalytic Reactions on the Open-Edge Sites of Nitrogen-Doped Carbon Nanotubes as Cathode Catalyst for Hydrogen Fuel Cells

Recent experimental reports proposed that pyridinic-type sites on the open edges of carbon nanotubes (CNTs) may contribute to the high catalytic activity for oxygen reduction reaction (ORR) on nitrogen-doped CNTs (N-CNTs). Herein, we performed first-principles spin-polarized density functional theory calculations to examine the catalytic steps for ORR and water formation reaction (WFR) on the open edges of N-CNTs. For half-N doping on the open edge of CNTs (HN-CNTs), O2 and OOH can be chemisorbed and partially reduced on the C–N bridge site without an energy barrier. The subsequent WFR for reduced O2/OOH with ambient H+ and additional electrons can be finished without energy barrier for the formation of two H2O molecules. The second H2O molecule needs an energy of ∼0.49 eV to be desorbed from the catalytic site, which completes an electrocatalytic reaction cycle on the cathode catalyst for hydrogen fuel cells (HFCs). For H-saturated open-edge sites of HN-CNT, ORR and WFR can also be completed energeticall...

Nitrogen-Doped Fullerene as a Potential Catalyst for Hydrogen Fuel Cells

We examine the possibility of nitrogen-doped C60 fullerene (N-C60) as a cathode catalyst for hydrogen fuel cells. We use first-principles spin-polarized density functional theory calculations to simulate the electrocatalytic reactions on N-C60. The first-principles results show that an O2 molecule can be adsorbed and partially reduced on the N-C complex sites (Pauling sites) of N-C60 without any activation barrier. Through a direct pathway, the partially reduced O2 can further react with H(+) and additional electrons and complete the water formation reaction (WFR) with no activation energy barrier. In the indirect pathway, reduced O2 reacts with H(+) and additional electrons to form H2O molecules through a transition state (TS) with a small activation barrier (0.22-0.37 eV). From an intermediate state to a TS, H(+) can obtain a kinetic energy of ∼0.95-3.68 eV, due to the Coulomb electric interaction, and easily overcome the activation energy barrier during the WFR. The full catalytic reaction cycles can be completed energetically, and N-C60 fullerene recovers to its original structure for the next catalytic reaction cycle. N-C60 fullerene is a potential cathode catalyst for hydrogen fuel cells.

First-principles investigation of adsorption of N2O on the anatase TiO2 (1 0 1) and the CO pre-adsorbed TiO2 surfaces

First-principles spin-polarized density functional theory computations in generalized gradient approximation to investigate the adsorption of N2O on the neutral and negative surfaces of the anatase TiO2 (101) and on the neutral and positive surfaces of CO pre-adsorbed TiO2 were carried out. The adsorption energies for N2O adsorbed on the TiO2 and the CO pre-adsorbed surfaces were obtained. Mechanisms for redox reaction of CO+N2O conversion to CO2+N2 on the neutral and positive TiO2 surfaces have been proposed and their photocatalytic involvement is described.

Atomic‐Level Elucidation of the Initial Stages of Self‐Assembled Monolayer Metallization and Nanoparticle Formation

The development of high-performance molecular electronics and nanotech applications requires deep understanding of atomic level structural, electronic, and magnetic properties of electrode/molecular interfaces. Recent electrochemical experiments on self-assembled monolayers (SAMs) have identified highly practical means to generate nanoparticles and metal monolayers suspended above substrate surfaces through SAM metallizations. A rational basis why this process is even possible is not yet well-understood. To clarify the initial stages of interface formation during SAM metallization, we used first-principles spin-polarized density functional theory (DFT) calculations to study Pd diffusion on top of 4-mercaptopyridine (4MP) SAMs on Au(111). After distinguishing potential-energy surfaces (PESs) for different spin configurations for transition metal atoms on the SAM, we find adatom diffusion is not possible over the clean 4MP-SAM surface. Pre-adsorption of transition-metal atoms, however, facilitates atomic diffusion that appears to explain multiple reports on experimentally observed island and monolayer formation on top of SAMs. Furthermore, these diffusions most likely occur by moving across low-lying and intersecting PESs of different spin states, opening the possibility of magnetic control over these systems. Vertical diffusion processes were also investigated, and the electrolyte was found to play a key role in preventing metal permeation through the SAM to the substrate.

Electronic structure and magnetic properties in Nitrogen-doped from density functional calculations

Abstract Based on first-principles spin-polarized density functional theory calculations, the electronic and magnetic properties of nitrogen-doped monoclinic β -phase gallium oxide are investigated. Calculations predict that the spin-polarized state is stable with a magnetic moment of about 1.0 μB per nitrogen-dopant. The magnetic moment mainly arises from the p orbital of nitrogen, with a little contribution from the Oxygen atoms surrounding it. Magnetic coupling between different nitrogen atoms is discussed, and the results show that the hole-mediated short-range p–p exchange mechanism is responsible for the predicted ferromagnetism. Calculations also reveal that experimentally observed red-shift should be N-2p gap states to band transition.

Electronic structure and magnetic interactions in Ni-doped β-Ga 2O 3 from first-principles calculations

Based on first-principles spin-polarized density functional theory calculations, the electronic structures and magnetic interactions of Ni-doped β -Ga 2 O 3 are investigated. Calculations predict that the spin-polarized state, with a magnetic moment of about 1.0 or 3.0 μ B per Ni-dopant when one Ni atom substitutes the octahedral or tetrahedral site, is more favorable in energy than that of non-spin polarized state. Ferromagnetic state, with an ordering temperature above room-temperature, is most stable for the structure in which one Ni substitutes the octahedral site.