Systematic First-principles Study Research Articles

Unveiling the physical properties of RbCu3MSe4 (M = Si, Ge) direct band gap semiconductors: A systematic first-principles study

The Silicon and Germanium-based quaternary chalcogenides have remarkable features including their adjustable optical properties and outstanding thermal stability. We explored the complex interplay among the structural, electronic, optical, and thermoelectric characteristics of direct band gap novel RbCu3MSe4 (M = Si, Ge) quaternary chalcogenides by employing the well-known density functional theory. Direct type of band gap at high symmetry Г-point was noticed for both materials. The predicted band gaps of RbCu3SiSe4 and RbCu3GeSe4 are 1.32 eV and 0.73 eV, respectively. Due to the large size of germanium ions compared to silicon, the Ge–Se bonds in RbCu3GeSe4 are more wide-ranging than the Si–Se bonds in RbCu3SiSe4. The complex dielectric function along with other significant optical parameters are investigated and analyzed for their probable employment for optoelectronic applications. These examined materials are suitable to be employed in thermoelectric devices as observed from substantial and outstanding thermoelectric features. The present work could establish the potential employment of these complex systems and would open the way for advanced applications in various fields and technologies.

Effect of Ta buffer layer on the structural and magnetic properties of stoichiometric intermetallic FeAl alloy

The magnetostructural phase transition in Fe50Al50 alloy with chemically ordered paramagnetic B2 and disordered ferromagnetic (FM) A2 phase has applications in spintronics such as phase-change magnetic memory and magnonic devices. We first conducted a systematic first-principles density functional theory study of the A2 and B2 phases in the Fe50Al50 alloy. A theoretical understanding of this equiatomic alloy’s electronic and spin-dynamical properties leads us to the experimental exploration of the FM A2 phase. Therefore, we deposit the 50 nm Fe50Al50 alloy thin film using sputtering and investigate the influence of the Ta buffer layer on its structural and magnetic properties. Our results reveal that the film with a buffer layer exhibits the A2 phase with appreciably higher saturation magnetization (848 emu/cc) than the film without a buffer layer (576 emu/cc). However, the surface roughness and Gilbert damping (α) slightly increase with the presence of the buffer layer from 0.41 to 0.56 nm and 4.35 × 10−3–4.94 × 10−3, respectively. The enhancement in α is due to extrinsic contributions induced by surface inhomogeneities.

First-principles study on structural, mechanical, electrical, optical and thermal properties of lithium- and calcium-based catalysts

This work presents a systematic first-principles study of the crystal structure, mechanical, electrical, optical, and thermodynamic properties of lithium- and calcium-based catalysts (Li3N, Ca3N2, Li3BN2, and Ca3B2N4) for the production of cubic boron nitride. The mechanical findings indicate that Ca3N2 is identified as a ductile material, with a higher B/G (20.04) and Poisson’s ratio (0.48). The other three materials are recognized as brittle materials, with B/G less than 1.75 and Poisson ratio less than 1/3. The electrical discoveries show that Li3BN2 has the widest band gap among the four catalyst materials, and the band gap of ternary catalyst materials (Li3BN2 and Ca3B2N4) is larger than that of corresponding binary catalyst materials (Li3N and Ca3N2). The optical results reveal that Li3N, Ca3N2, Li3BN2, and Ca3B2N4 have sufficient energy to prevent charge carriers from being scattered or captured by material defects. The absorption peaks of Ca-based materials (Ca3N2 and Ca3B2N4) are significantly higher than those of Li-based materials (Li3N and Li3BN2). In this frequency range, the light is the most difficult to pass through in Ca3N2 and the easiest to propagate in Ca3B2N4. The connection between Li3N and Ca3N2 bands is greater, while the Li3BN2 and Ca3B2N4 bands interact rather weakly. The thermodynamic conclusions demonstrate that the thermal stability of the four structures is as follows: Li3N< Ca3N2< Li3BN2< Ca3B2N4. The heat capacities of Li3N, Ca3N2, Li3BN2, and Ca3B2N4 tend to approach 23.74, 52.05, 70.73, and 311.48 J·mol−1·K−1, respectively.

Magnetic interactions in intercalated transition metal dichalcogenides: A study based on ab initio model construction

Transition metal dichalcogenides (TMDs) are known to have a wide variety of magnetic structures by hosting other transition metal atoms in the van der Waals gaps. To understand the chemical trend of the magnetic properties of the intercalated TMDs, we perform a systematic first-principles study for 48 compounds with different hosts, guests, and composition ratios. Starting with calculations based on spin density functional theory, we derive classical spin models by applying the Liechtenstein method to the ab initio Wannier-based tight-binding model. We show that the calculated exchange couplings are overall consistent with the experiments. In particular, when the composition rate is 1/3, the chemical trend can be understood in terms of the occupation of the 3d-orbital in the intercalated transition metal. The present results give us a useful guiding principle to predict the magnetic structure of compounds that are yet to be synthesized.

Bandgap Engineering of Two-Dimensional Double Perovskite Cs4AgBiBr8/WSe2 Heterostructure from Indirect Bandgap to Direct Bandgap by Introducing Se Vacancy.

Heterostructures based on layered materials are considered next-generation photocatalysts due to their unique mechanical, physical, and chemical properties. In this work, we conducted a systematic first-principles study on the structure, stability, and electronic properties of a 2D monolayer WSe2/Cs4AgBiBr8 heterostructure. We found that the heterostructure is not only a type-II heterostructure with a high optical absorption coefficient, but also shows better optoelectronic properties, changing from an indirect bandgap semiconductor (about 1.70 eV) to a direct bandgap semiconductor (about 1.23 eV) by introducing an appropriate Se vacancy. Moreover, we investigated the stability of the heterostructure with Se atomic vacancy in different positions and found that the heterostructure was more stable when the Se vacancy is near the vertical direction of the upper Br atoms from the 2D double perovskite layer. The insightful understanding of WSe2/Cs4AgBiBr8 heterostructure and the defect engineering will offer useful strategies to design superior layered photodetectors.

Iodine Vacancies do not Cause Nonradiative Recombination in Halide Perovskites

A systematic first-principles study shows that the iodine vacancy does not lead to strong nonradiative losses in halide perovskites as commonly believed; thus, performance optimization strategies for perovskite solar cells should focus on other defects.

Nonlinear optical properties of superalkali@teetotum boron clusters with potential applications on the electro-optic modulator

The development of nonlinear optics has revolutionized the photonic and optoelectronic fields in recent years.In this paper, we have designed a new class of donor–acceptor frameworks with enhanced nonlinear optical (NLO)properties using a series of superalkalis including Li3O, Li2NaO, LiNa2O, Li2KO, LiK2O as donors and three sizes of teetotum boron clusters (B14, B18, and B22) as acceptors. A systematic first-principles study has been performed on the electronic, linear, and NLO properties of superalkali@Bnassemblies. Besides the static non-linearity, the frequency-dependent electro-optic Pockel's effect (EOPE), second harmonic generation (SHG), and nonlinear refractive index have also been evaluated. In the case of dynamic NLO, the SHG process has a stronger NLO response than EOPE. At the typical experimental frequency of the Nd:YAG laser (ω = 0.04282) a.u., the SHG coefficients are about 2–3 times larger than the corresponding EOPE at this wavelength. Also, the nonlinear refractive index shows a remarkable response atω = 0.04 a.u. for LiK2O@B14.

The rendering from the periodic system of elements on the stability, elastic, and electronic properties of M2AC phases

MAX phases are nanolaminated ternary materials that combine metallic and ceramic properties. Currently, the A-site elements replacement in traditional ones by later transition-metals opens a door to explore new types of MAX phases. In this work, we performed a systematic first-principle study to explore trends in stability, electronic structure and elastic properties of 288 compositions of M2AX phases (M=Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W; A=Al, Si, P, S, Ga, Ge, As, Se, In, Sn, Sb, Te, Tl, Pb, Bi, Mn, Fe, Co, Ni, Cu, Zn, Tc, Ru, Rh, Pd, Ag, Cd, Os, Ir, Pt, Au, Hg; X=C). Such a dataset, combined with the rigid-band model been applied to most transition metal carbides, shows us the fundamental trends in bonding mechanisms and elastic properties of MAX phases endowed with the periodic arrangements of M/A-site elements. In particular, the M-A d-d interactions of MAX phases uniquely contribute to the elastic constant C33.

Remarkable enhancement in catechol sensing by the decoration of selective transition metals in biphenylene sheet: A systematic first-principles study

Motivated by the recent successful synthesis of biphenylene structure (Fan et al 2021 Science 372 852), we have explored the sensing properties of this material towards the catechol biomolecule by performing the first-principles density functional theory and molecular dynamics simulations. Pristine biphenylene sheet adsorbs catechol molecule with a binding energy of −0.35 eV, which can be systematically improved by decorating the transition metals (Ag, Au, Pd, and Ti) at various possible sites of biphenylene. It is observed that the catechol molecule is adsorbed on Pd and Ti-decorated biphenylene sheets with strong adsorption energies of −1.00 eV and −2.54 eV, respectively. The interaction of the catechol molecule with biphenylene and metal-decorated biphenylene is due to the charge transfer from the O-2p orbitals of the catechol molecule to the C-2p orbitals of biphenylene and d-orbitals of metals in metal-decorated biphenylene, respectively. From the Bader charge calculation, we found that 0.05e amount of charge is transferred from the catechol molecule to pristine biphenylene, which gets almost double (∼0.1e) for the Ti-decorated biphenylene sheet. The diffusion energy barrier for the clustering of the Pd and Ti atoms comes out to be 2.39 eV and 4.29 eV, computed by performing the climbing-image nudged elastic band calculations. We found that the catechol molecule gets desorbed from the pristine biphenylene sheet at 100 K but remains attached to metal (Pd, Ti) decorated biphenylene sheets at room temperature by performing the ab-initio molecular dynamics simulations. The Ti-decorated biphenylene sheet has more sensitivity toward catechol adsorption while the Pd-decorated biphenylene sheet has a suitable recovery time at 500 K. The results suggest that the Pd and Ti-decorated biphenylene sheets are promising materials for catechol detection.

High capacity hydrogen storage on zirconium decorated γ-graphyne: A systematic first-principles study

In this work, we investigate the hydrogen-storage properties of Zr-decorated γ-graphyne monolayer employing Density Functional Theory (DFT) for green energy storage. We predict that each Zr atom decorated on graphyne sheet (2D) can adsorb up to seven H2 molecules with an average adsorption energy of −0.44 eV/H2, leading to a hydrogen gravimetric density of 7.95 wt%, and desorption temperature of 574 K, particularly suited to fuel-cell applications. Decorated Zr atom strongly attached to graphyne due to charge transfer from Zr to graphyne sheet. Hydrogen molecules adsorb on Zr decorated graphyne due to Kubas type of interactions. The 4.05 eV diffusion energy barrier for the movement of Zr atoms may avoid the metal-metal (Zr–Zr) clustering. The stability of Zr+γ-graphyne is confirmed by performing ab-initio molecular dynamics simulations at room temperature and at estimated average desorption temperature. Hence, our calculations show that Zr functionalized on γ-graphyne could be a promising solid-state hydrogen storage material.

The electronic structure and elastic properties of NbSiSb and NbGeSb: A first-principles study

A systematic first-principles study on crystal and electronic structure and elastic properties of NbXSb (X = Ge, Si) is carried out using density functional theory (DFT). The results on atomic bonding show that the main bonding is covalent bonds for both NbSiSb and NbGeSb. Both materials show abundant band structures. The calculated bulk band and density of states with and without the spin-orbit coupling effect (SOC) suggest that SOC leads to the band gaps opening around the Fermi level. Further analysis of the slab model with different layers reveals a topologically protected Dirac cone near the Fermi level in NbGeSb. Moreover, the brittleness of NbSiSb is larger than NbGeSb, and the anisotropy of elastic moduli decreases when Si replaces Ge. This work may provide new inspiration and ideas for understanding the behaviour of topological materials.

First principles investigation on Li or Sn codoped hexagonal tungsten bronzes as the near-infrared shielding material

The 52% energy of the solar radiation is contributed by near-infrared radiation (NIR, 780–2500 nm). Therefore, the material design for the energy-saving smart window, which can effectively shield NIR and has acceptable visible transmittance, is vital to save the energy consumed on the temperature control system. It is important to find a non-toxic stable material with excellent NIR-shielding ability and acceptable visible transmittance. The systematic first-principles study on Li x Sn y WO3 (x = 0, 0.33, 0.66, and y = 0, 0.33) exhibits that the chemical stability is a positive correlation with the doping concentration. After doping, the Fermi-energy upshifts into the conduction band, and the material shows metal-like characteristics. Therefore, these structures Li x Sn y WO3 (except the structure with x = 0.33 and y = 0) show pronounced improvement of NIR shielding ability. Our results indicate that when x = 0 and y = 0.33, the material exhibits the strongest NIR-shielding ability, satisfying chemical stability, wide NIR-shielding range (780–2500 nm), and acceptable visible transmittance. This work provides a good choice for experimental study on NIR shielding material for the energy-saving window.

Superconductivity and topologically nontrivial states in noncentrosymmetric XVSe2 (X = Pb, Sn): a first-principles study.

Noncentrosymmetric superconductors are strong candidates for exploring intrinsic topological superconductivity. Here, we predict two new noncentrosymmetric superconductors SnVSe2 and PbVSe2 by a systematic first-principles study. These two compounds show good thermal and dynamic stabilities. Moreover, the band topology of both compounds is predicted to be nontrivial via Z2 calculation and slab models. We also investigate the electron-phonon interactions in SnVSe2 and PbVSe2, indicating the Tc of SnVSe2 and PbVSe2 without external pressure are predicted to be ∼1.18 K and ∼0.22 K, respectively. Furthermore, the results on pressure engineering in PbVSe2 imply that the Tc of PbVSe2 can be tuned to 2.39 K for enhanced contributions from Pb layers under pressure up to 6.4 GPa. This work may provide new platforms for probing spin-triplet paring and may help with designing and developing new metal-intercalated transition metal dichalcogenides.

Li-rich channels as the material gene for facile lithium diffusion in halide solid electrolytes

Halide solid electrolytes have attracted intense research interest recently for application in all-solid-state lithium-ion batteries. Herein, we present a systematic first-principles study of the Li3MX6 (M: multivalent cation; X: halogen anion) halide family that unveils the link between Li-rich channels and ionic conductivity, highlighting the former as a material gene in these compounds. By screening a total of 180 halides for those with high thermodynamic stability, wide electrochemical window, low chemical reactivity, and decent Li-ion conductivity, we identify seven unexplored candidates for solid electrolytes. From these halides and another four prototype compounds, we discover that the facile Li diffusion is rooted in the availability of diffusion pathways which can avoid direct connection with M cations—that is, where the local environment is Li-rich. These findings shed light on strategies for regulating cation and anion frameworks to establish Li-rich channels in the design of high-performance inorganic solid electrolytes.

Magnetic properties of 3d, 4d, and 5d transition-metal atomic monolayers in Fe/TM/Fe sandwiches: Systematic first-principles study

Previous studies have accurately determined the effect of transition metal point defects on the properties of bcc iron. The magnetic properties of transition metal monolayers on the iron surfaces have been studied equally intensively. In this work, we investigated the magnetic properties of the 3d, 4d, and 5d transition-metal (TM) atomic monolayers in Fe/TM/Fe sandwiches using the full-potential local-orbital (FPLO) scheme of density functional theory. We prepared models of Fe/TM/Fe structures using the supercell method. We selected the total thickness of our system so that the Fe atomic layers furthest from the TM layer exhibit bulk iron-bcc properties. Along the direction perpendicular to the TM layer, we observe oscillations of spin and charge density. For Pt and W we obtained the largest values of perpendicular magnetocrystalline anisotropy and for Lu and Ir the largest values of in-plane magnetocrystalline anisotropy. All TM layers, except Co and Ni, reduce the total spin magnetic moment in the generated models, which is in good agreement with the Slater-Pauling curve. Density of states calculations showed that for Ag, Pd, Ir, and Au monolayers, a distinct van Hove singularity associated with TM/Fe interface can be observed at the Fermi level.

Adsorption of La on kaolinite (0 0 1) surface in aqueous system: A combined simulation with an experimental verification

A systematic first-principles model study of La(III) adsorption on kaolinite (001) surface was studied using periodic DFT calculations. The effective coordination number, coordination geometry, preferred adsorption position and adsorption type were examined. Based on the binding energy, the form of [La(OH)(H2O)8]2+ would be more stable than [La(H2O)10]3+ in a high pH solution system. Outer-layer and inner-layer adsorption models were applied to account for the different bonding between La and the kaolinite surface. The inner-layer adsorption model was dominated by coordination bonds between La and surface oxygen, while the outer-layer adsorption model was related to hydrogen bonds. The inner-layer adsorption at the Ou site was the optimal adsorption site. The PDOS projections and Mulliken bond populations suggest that the bonding orbital combination of La 5d and Ou 2p was the dominant orbital contribution of La-Ou. Contrary to the stability of La ions in aqueous systems, [La(H2O)10]3+ would be more stable than [La(OH)(H2O)8]2+ after adsorption on the kaolinite (001) surface, which was verified by microcalorimetry experiments.

Strong bulk photovoltaic effect and second-harmonic generation in two-dimensional selenium and tellurium

Few-layer selenium and tellurium films have been recently prepared, and they provide a new platform to explore novel properties of two-dimensional (2D) elemental materials. In this work, we have performed a systematic first-principles study on the electronic, linear, and nonlinear optical (NLO) properties of atomically thin selenium and tellurium films within the density-functional theory with the generalized gradient approximation plus scissors correction using the band gaps from the relativistic hybrid Heyd-Scuseria-Ernzerhof functional calculations. Interestingly, we find that few-layer Se and Te possess large second-harmonic generation (SHG), linear electro-optic effect, and bulk photovoltaic effect. In particular, trilayer (TL) Te possesses large SHG coefficient, being more than 65 times larger than that of GaN, a widely used NLO material. Bilayer (BL) Te has huge static SHG coefficient, being more than 100 times larger than that of GaN. Furthermore, monolayer (ML) Se possesses large SHG coefficient. Moreover, we predict that TL Te exhibits strong bulk photovoltaic effect (BPVE), being greater than that of GeS, a polar system with the largest BPVE found so far. Although the shift current conductivities of bulk and 2D Se are comparable, the shift current conductivities of TL Te are five times larger than those of bulk Te. Finally, an analysis of the calculated electronic band structures indicates that the strong NLO responses of 2D Se and Te materials are primarily derived from their low-dimensional structures with high anisotropy, directional covalent bonding, lone-pair electrons, and relatively small band gaps. These findings provide a practical strategy to search for excellent NLO and BPVE materials.

Muonium behavior in N-acetylglycine-N-methylamide

In muon spin rotation and relaxation (mSR) method, theoretical work using first-principles calculations helps to understand the stopping sites and charge states of muon in the sample materials. To support the mSR measurement on protein and DNA, a systematic first-principles study starting from the constituents of the protein has been performed. In this work, the behavior of muonium (Mu = m+e-, bound state of a muon and an electron which is like a light isotope of H atom with similar chemical properties) in a N-acetylglycine-N-methylamide (AGMA), a part of peptide bond, is presented. It is found that the stopping site of Mu is around O of unsaturated bonds between C and O in the AGMA. Further calculations towards whole protein and DNA will be performed to support mSR studies.&#x0D; BIBECHANA 18 (2) (2021) 138-142

Origin of Water-Induced Deactivation of MnO2-Based Catalyst for Room-Temperature NO Oxidation: A First-Principles Microkinetic Study

MnO2-based catalysts exhibit remarkable activities in a room-temperature NO oxidation reaction (RT-NOR) but are challenged by water-induced deactivation. To improve the water-resistance driven by molecular-level mechanistic understanding, we herein report a systematic first-principles study and microkinetic simulation on elucidating the water-modulated RT-NOR mechanism on the notable β-MnO2 catalyst. Results show that RT-NOR preferentially follows the Mars-van Krevelen mechanism on β-MnO2(110) and that the coupling of lattice O (Olat) with NO sitting on the surface Mncus site is the rate-limiting step. The presence of H2O results in a competitive effect against NO adsorbing on Mncus and inhibits NO2 formation. More crucially, the H2O-dissociated H species eventually accumulate on Olat and are difficult to remove, which seriously poison the catalyst, although the Mncus-anchored OH intermediate can oxidize NO to NO2 via the nitrite/nitrate route. Weakening the H adsorption on Olat, as well as the H2O adsorption on Mncus, is thus proposed as conductive to alleviating MnO2 deactivation. More essentially, we find that the vacancy formation energy of Olat, Ef(Ovac), can serve as a unified descriptor for balancing H2O-resistance and catalytic activity; the excessively low Ef(Ovac) is the intrinsic origin of MnO2 susceptible to deactivation by H2O. By doping engineering guided by such a descriptor, we identify that the Cr-, Nb-, Ru-, or Rh-substituted doping can properly increase the Ef(Ovac) of MnO2 and weaken the H2O-induced deactivation in RT-NOR. These results may provide a theoretical basis on optimizing MnO2-based catalysts with improved H2O-resistance.

Optimization of Doping CdTe with Group-V Elements: A First-Principles Study

Group-V substitution at the $\mathrm{Te}$ site, ${X}_{\mathrm{Te}}$ (X = $\mathrm{P}$, $\mathrm{As}$, $\mathrm{Sb}$), under $\mathrm{Cd}$-rich conditions is an effective way to enhance the hole density and, in the meantime, suppresses the dominant nonradiative carrier recombination center in $\mathrm{Cd}\mathrm{Te}$, thus, improving the performance of $\mathrm{Cd}\mathrm{Te}$ thin-film solar cells. However, it is not clear which group-V dopant, X, is the most effective dopant, because it is expected that ${\mathrm{P}}_{\mathrm{Te}}$ will have the shallowest acceptor level due to its high electronegativity, whereas ${\mathrm{Sb}}_{\mathrm{Te}}$ will have the smallest formation energy due to its small size mismatch with $\mathrm{Te}$. Our systematic first-principles study shows that the hole concentration contributed by the acceptor ${X}_{\mathrm{Te}}^{\ensuremath{-}}$ is limited by the related compensating $A{X}^{+}$ center that increases simultaneously with ${X}_{\mathrm{Te}}^{\ensuremath{-}}$ as the chemical potential of dopant X increases. However, the ratio of ${X}_{\mathrm{Te}}^{\ensuremath{-}}$ acceptors to the $A{X}^{+}$ donors can be significantly increased if the sample is grown at high temperature and then annealed to room temperature, achieving a high hole density and low Fermi level $({E}_{F})$. We find that all group-V ($\mathrm{P}$, $\mathrm{As}$, and $\mathrm{Sb}$) dopings can achieve maximum hole densities of about ${10}^{17}\phantom{\rule{0.25em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$, which are consistent with previous experimental results. Despite the relatively deep acceptor level of 150 meV, $\mathrm{Sb}$ doping can achieve a considerable hole density due to the low formation energy of substituting $\mathrm{Sb}$ for $\mathrm{Te}$ with similar atomic radii. $\mathrm{P}$ doping can achieve a higher hole density than that of $\mathrm{Sb}$ due to its shallow transition energy at \ensuremath{\epsilon}(0/\ensuremath{-}) = 70 meV. However, the highest hole density is achieved through $\mathrm{As}$ doping, which is attributed to its balanced defect level at \ensuremath{\epsilon}(0/\ensuremath{-}) = 80 meV and relatively small formation energy.