First-principles Calculations Research Articles

Effect of anion (S−2 & Se−2) replacement on photovoltaic properties in transition metal (Ba-Barium) chalcogenide perovskites

Material scientists have stepped up their search for efficient materials in low-cost, high-stability, nontoxic energy conversion devices. In this paper, emerging materials inspire us to study one of the perovskite chalcogens made from alkaline-earth metals (Barelium). Therefore, we determined some fundamental properties with some application-based properties, which explained their applicability in energy conversion device fabrication by first-principles calculation within the WIEN2K Code. Structure stability has been verified by Birch–Murnaghan fits and thermal stability at different temperatures and pressure ranges is explained by Gibbs function in thermodynamic properties. By using modified Becke–Johnson (mBJ) potential, electronic and optical characteristics of these materials provide insight into their nature: they were revealed to be direct bandgap semiconductors with the calculated values of 1.77[Formula: see text]eV (1.25[Formula: see text]eV) for BaZrS3(BaZrSe3), respectively. Both materials exhibit transparency on low-energy striking photons and demonstrate absorption and optical conduction in the UV region. Both materials exhibit transparency on low-energy striking photons and demonstrate absorption and optical conduction in the UV region. In the thermoelectric parameter, the figure of merit (ZT) is unity at room temperature and decreases up to 0.98 with temperature increment which reveals that these materials will be helpful in thermoelectric devices. As per the application part, we carried out the calculation of the spectroscopic limited maximum efficiency (SLME) and found that efficiency increases from 6.5% to 27.1% (8.1% to 31.9%) for BaZrS3 (BaZrSe3), respectively. The film thickness increased from 100[Formula: see text]nm to 1[Formula: see text][Formula: see text]m at room temperature and then stabilized. This emerging study shows that these materials can be used as an alert substance in energy conversion device fabrications and the proposed outcomes are in good acceptance with the experimental and other theoretical data. As per the optical and thermoelectric parameters of these materials, we infer that both are promising candidates in energy conversion device fabrication.

Exploring the Molecular-Scale Structures at Solid/Liquid Interfaces of Li-Ion Battery Materials: A Force Spectroscopy Analysis with Sparse Modeling.

In this study, we clarify the liquid structure formed at the interface between LiCoO2 (LCO), the cathode material of Li-ion batteries, and propylene carbonate (PC), which is used as a solvent in the electrolyte, on a molecular scale. We apply sparse modeling-based modal analysis to force spectroscopy data measured by frequency modulation atomic force microscopy (FM-AFM) and show that each component in the FM-AFM force curve, such as oscillatory solvation force, background, and noise, can be automatically decomposed. Moreover, by combining detailed force curve analysis with solid/liquid interface simulations based on first-principles calculation, we have identified that there are distinct damped vibrational modes in the force curves at the LCO/PC interface with a period of about 0.57 nm and those with shorter periods, which likely correspond to the solvation forces associated with bulk-state PC molecules and those with PC molecules in "lying down" orientations.

Strain Engineering of Ion-Coordinated Nanochannels in Nanocellulose.

Expanding the interlayer spacing plays a significant role in improving the conductivity of a cellulose-based conductor. However, it remains a challenge to regulate the cellulose nanochannel expanded by ion coordination. Herein, starting from multiscale mechanics, we proposed a strain engineering method to regulate the interlayer spacing of the cellulose nanochannels. First-principles calculations were conducted to select the most suitable ions for coordination. Large-scale molecular dynamics simulations were performed to reveal the mechanism of interlayer spacing expansion by the ion cross-linking. Combining the shear-lag model, we established the relationship between interfacial cross-link density and interlayer spacing of an ion-coordinated cellulose nanochannel. Consequently, fast ion transport and current regulation were realized via the strain engineering of nanochannels, which provides a promising strategy for the current regulation of a cellulose-based conductor.

Investigating the structural, electronic, and magnetic properties of Cd1-xVxTe: Insights from First-Principles calculations

In our study, we aim to investigate the structural, electronic, and magnetic properties of CdVTe, a diluted magnetic semiconductor with a Cadmium telluride (CdTe) structure. To achieve this, we employ the full potential linear augmented plane wave method implemented in the CASTEP code, which allows us to accurately simulate the behavior of the system. To describe the electronic exchange and correlation effects, we adopt the generalized gradient approximation (GGA) within the density functional theory (DFT) framework. This choice of methodology ensures reliable and accurate calculations of the electronic and magnetic properties of Cd1-xVxTe. Our results reveal that the substitution of Vanadium (V) into the Cadmium (Cd) site of the CdTe lattice does not alter the zinc blende crystal structure, demonstrating the stability and structural integrity of the system. Furthermore, our calculations demonstrate that the introduction of Vanadium impurities leads to spin polarization within the material, resulting in the emergence of a magnetic moment. Notably, we find that a Vanadium concentration of approximately x≈0.12 exhibits the strongest magnetic properties, characterized by a significant magnetic moment. These findings provide valuable insights into the behavior and potential applications of CdVTe as a diluted magnetic semiconductor, shedding light on the interplay between structural, electronic, and magnetic properties in this material.

Signature of excitonic insulators in phosphorene nanoribbons.

Phosphorene is a recently developed two-dimensional (2D) material that has attracted tremendous attention because of its unique anisotropic optical properties and quasi-one-dimensional (1D) excitons. We use first-principles calculations combined with the maximally localized Wannier function tight binding Hamiltonian (MLWF-TB) and Bethe-Salpeter equation (BSE) formalism to investigate quasiparticle effects of 2D and quasi-1D blue and black phosphorene nanoribbons. Our electronic structure calculations shows that both blue and black monolayered phases are semiconductors. On the other hand black phosphorene zigzag nanoribbons are metallic. Similar behavior is found for very thin blue phosphorene zig-zag and armchair nanoribbon. As a general behavior, the exciton binding energy decreases as the ribbon width increases, which highlights the importance of quantum confinement effects. The solution of the BSE shows that the blue phosphorene monolayer has an exciton binding energy four times higher than that of the black phosphorene counterpart. Furthermore, both monolayers show a different linear optical response with respect to light polarization, as black phosphorene is highly anisotropic. We find a similar, but less pronounced, optical anisotropy for blue phosphorene monolayer, caused exclusively by the quasi-particle effects. Finally, we show that some of the investigated nanoribbons show a spin-triplet excitonic insulator behavior, thus revealing exciting features of these nanoribbons and therefore provides important advances in the understanding of quasi-one dimensional phosphorus-based materials.&#xD.

Tuning Electronic and Structural Properties of Lead-Free Metal Halide Perovskites: A Comparative Study of 2D Ruddlesden-Popper and 3D Compositions.

In recent decades, two-dimensional (\num{2}D) perovskites have emerged as promising semiconductors for next-generation photovoltaics, showing notable advancements in solar energy conversion. Herein, we explore the impact of alternative inorganic lattice \ce{BX}-based compositions ($\ce{B} = \ce{Ge}$ or \ce{Sn}, $\ce{X} = \ce{Br}$ or \ce{I}) on the energy gap and stability. Our investigation encompasses \ce{BA$_2$MA$_{n-1}$B$_n$X$_{3n+1}$} \num{2}D Ruddlesden-Popper perovskites (for $n = \num{1} - \num{5}$ layers) and \num{3}D bulk \ce{(MA)BX$_3$} systems, employing first-principles calculations with spin-orbit coupling (SOC), DFT-1/2 quasiparticle, and D3 dispersion corrections. The study unveils how atoms with smaller ionic radii induce anisotropic internal and external distortions within the inorganic and organic lattices. Introducing the \ce{BA} spacers in the low-layer regime reduces local distortions but widens band gaps. Our calculation protocol provides deeper insights into the physics and chemistry underlying \num{2}D perovskite materials, paving the way for optimizing environmentally friendly alternatives that can efficiently replace \ce{Pb} with sustainable materials.

Properties of the chalcogenide-based double perovskites Ba2NbBiS6 and Ba2TaSbS6 with respect to structural, electronic and optical aspects

In this work, we delve into the investigation of the structural, electronic, and optical properties of Ba2NbBiS6 and Ba2TaSbS6 chalcogenide-based double perovskites, which are structured in the cubic space group [Formula: see text] form. We have performed first-principles calculations using density functional theory (DFT) to study the above properties. The electronic band structure and density of states of this compound have been investigated, and their results show that Ba2NbBiS6 and Ba2TaSbS6 exhibit a semiconducting nature with an indirect energy gap of 1.680[Formula: see text]eV and 1.529[Formula: see text]eV, respectively. Furthermore, an investigation was conducted on the optical properties of the compounds throughout the energy range spanning from 0[Formula: see text]eV to 55[Formula: see text]eV. This investigation focused on many parameters, including dielectric functions, optical reflectivity, refractive index, extinction coefficient, optical conductivity, and electron energy loss. The optical data obtained from the calculations reveals that all compounds demonstrate isotropy in optical polarization. Furthermore, it has been noted that our compounds exhibit absorption properties inside the ultraviolet (UV) region. Consequently, these materials hold promise as potential candidates for various applications, such as UV photodetectors, UV light emitters, and power electronics. This is primarily attributed to their inherent absorption limits and the presence of prominent absorption peaks in this spectral range. In brief, chemical mutation techniques have been employed to manipulate the characteristics of double-sulfide perovskites to develop durable and environmentally friendly perovskite materials suitable for solar purposes.

Anisotropic optical property of ferroelectric Bi2O2X (X=S,Se,Te) monolayer and strain engineering.

Based on the first-principles calculations, ferroelectric Bi2O2X (X=S, Se, Te) monolayers with unequivalent in-plane lattice constants are confirmed to be the ground state, which is consistent with the experiment result (Nano Lett. 19, 5703(2019)), and the anisotropic optical property is firstly investigated. We find that the polarizations of Bi2O2X monolayers points along the direction of a-axis, and Bi2O2T e monolayer process the largest polarization. Furthermore, both the biaxial and uniaxial strains are favor for the enhancement of polarization of Bi2O2X monolayers. It should be mentioned that the type of band gap will convert from indirect to direct for Bi2O2T e monolayer when the a-axial tensile strain is larger than 2%. At last, the optical absorption coefficient for Bi2O2X monolayers are calculated, and we obtain that Bi2O2Te monolayer has the strongest optical absorption within the range of visible light, the anisotropy and possible strain engineering to improve the optical absorption are discussed in detail. Our findings are significant in fields of optoelectronics and photovoltaics.&#xD.

Anisotropic optoelectronic properties of lead-free Cs3Bi2I9 single-crystal photodetectors

Abstract Lead-free halide perovskites have attracted widespread research interest due to their excellent optoelectronic properties and environmental friendliness. As one of the bismuth iodide compounds, Cs3Bi2I9 perovskite has been extensively explored in the field of photovoltaic devices and radiation detectors due to their non-toxic lead-free components and excellent stability. In this work, we successfully grow large-sized Cs3Bi2I9 single crystals (SC) with (l00) and (00l) crystal exposure facets by inverse temperature crystallization method. Under 525 nm light illumination with the intensity 15 mW/cm2 and 7 V bias, the (l00) Cs3Bi2I9 SC shows 2 times higher photocurrent, 3.6 times higher responsivity, and 2.8 times higher detectivity than the (00l) Cs3Bi2I9 SC, respectively. Superior response time in the scale of millisecond is obtained in both (l00) and (00l) Cs3Bi2I9 SCs. Based on the first-principle calculation, the (l00) SC possesses a higher charge distribution density and a wider dispersion distribution than (00l) SC, suggesting that more electrons in the (l00) SC can be excited in a wider range. The tighter arrangement of Cs+ and [BiI6]− octahedra in the (l00) SC than (00l) SC leads to the anisotropic photoelectric performance in (l00) and (00l) Cs3Bi2I9 SCs. Our results provide a strategy for the oriental growth of Cs3Bi2I9 SCs and the design of anisotropic optoelectronic devices with excellent performance.

Anatomy of Hidden Dzyaloshinskii-Moriya Interactions and Topological Spin Textures in Centrosymmetric Crystals.

The Dzyaloshinskii-Moriya interaction (DMI) is understood to be forbidden by the symmetry of centrosymmetric systems, thus restricting the candidate types for investigating many correlated physical phenomena. Here, we report the hidden DMI existing in centrosymmetric magnets driven by the local inversion symmetry breaking of specific spin sublattices. The opposite DMI spatially localized on the inverse spin sublattice favors the separated spin spiral with opposite chirality. Furthermore, we elucidate that hidden DMI widely exists in many potential candidates, from the first-principles calculations on the mature crystal database. Interestingly, novel topological spin configurations, such as the anti-chirality-locked merons and antiferromagnetic-ferromagnetic meron chains, are stabilized as a consequence of hidden DMI. Our understanding enables the effective control of DMI by symmetry operations at the atomic level and enlarges the range of currently useful magnets for topological magnetism.

Hidden Real Topology and Unusual Magnetoelectric Responses in Two-Dimensional Antiferromagnets.

Recently, the real topology has been attracting widespread interest in two dimensions (2D). Here, based on first-principles calculations and theoretical analysis, the monolayer Cr2Se2O (ML-CrSeO) is revealed as the first material example of a 2D antiferromagnetic (AFM) real Chern insulator (RCI) with topologically protected corner states. Unlike previous RCIs, it is found that the real topology of the ML-CrSeO is rooted in one certain mirror subsystem of the two spin channels, and cannot be directly obtained from all the valence bands in each spin channel as commonly believed. In particular, due to antiferromagnetism, the corner modes in ML-CrSeO exhibit strong corner-contrasted spin polarization, leading to spin-corner coupling (SCC). This SCC enables a direct connection between spin space and real space. Consequently, large and switchable net magnetization can be induced in the ML-CrSeO nanodisk by electrostatic means, such as potential step and in-plane electric field, and the corresponding magnetoelectric responses behave like a sign function, distinguished from that of the conventional multiferroic materials. This work considerably broadens the candidate range of RCI materials, and opens up a new direction for topo-spintronics and 2D AFM materialsresearch.

Rational design of hollow C@SnS2/SnS@C cubes with N-doping to realize stepwise sodium storage induced structural stability for highly stable cycling performance

Current application of SnS2-based anodes in sodium-ion batteries fails to meet the demand for higher Na+ storage capacity due to the structural pulverization induced by significant volume changes during cycling. Herein, a novel composite of hollow C@SnS2/SnS@C cubes with excellent diffusion kinetics and structural stability from stepwise Na+ storage is designed. The SnS with gentle pseudocapacitive reaction acts as the self-supporter to prevent the collapse of SnS2/SnS heterostructure during the Na+ insertion/extraction. Together with the clamping of double carbon layers and hollow construction, the volume change caused structural instability in heterostructure is effectively alleviated. The rapid transport of electrons and ions within the built-in electric field of heterostructure endows the composite an excellent diffusion kinetics, which is generated from the narrow bandgap and outstanding Na+ absorption of heterostructure according to the first-principle calculation. Thus, the as-prepared composite maintains a remarkable capacity of 547.9 mAh g−1 after 200 cycles at current density of 0.5 A g−1. Even a capacity of 502.5 mAh g−1 with a low attenuation rate of 0.035 % per cycle is achieved at 2 A g−1 after 1000 cycles. The work proposes an effective approach to achieve effective Na + storage of SnS2-based anodes with long-lasting structural stability.

(C8H7N2O2)2[Bi2Br8]·2H2O and (C8H7N2O2)6[Bi2Cl10]Cl2·2H2O: Exploring Birefringent Crystals in Hybrid Halide Systems.

In this study, new hybrid birefringent crystals of (C8H7N2O2)2[Bi2Br8]·2H2O and (C8H7N2O2)6[Bi2Cl10]Cl2·2H2O were successfully synthesized by introducing a new birefringent group [C8H7N2O2]+ by a simple aqueous solution evaporation method. They crystallize in the P21/n space group, and their structure consists mainly of the π-conjugated group [C8H7N2O2]+ and the octahedron centered on Bi3+. By first-principles calculations, the birefringence response comes from the [C8H7N2O2]+ group with a planar π-conjugated structure. Meanwhile, the synthesis, structure, first-principles calculations, and optical properties are reported in this paper.

Ion solvation free energy calculations based on first-principles molecular dynamics thermodynamic integration.

Numerous electrochemistry reactions require the precise calculation of the ion solvation energy. Despite the significant progress in the first-principles calculations for crystals and defect formation energies for solids, the liquid system free energy calculations still face many challenges. Ion solvation free energies can be calculated via different semiempirical ways, e.g., using implicit solvent models or cluster of explicit molecule models; however, systematically improving these models is difficult due to their lack of a solid theoretical base. A theoretically sound approach for calculating the free energy is to use thermodynamic integration. Nevertheless, owing to the difficulties of self-consistent convergence in first-principles calculations for unphysical atomic configurations, the computational alchemy approach has not been widely used for first-principles calculations. This study proposes a general approach to use first-principles computational alchemy for calculating the ion solvation energy. This approach is also applicable for other small molecules. The calculated ion solvation free energies for Li+, Na+, K+, Be2+, Mg2+, and Ca2+ are close to the experimental results, and the standard deviation due to molecular dynamics fluctuations is within 0.06eV.

Long-Range Influence of Cr on the Stacking Fault Energy of Cr-Containing Concentrated Solid-Solution Alloys

Single-phase concentrated solid-solution alloys (CSAs) have exhibited excellent mechanical and radiation tolerance properties, making them potential candidate materials for nuclear applications. These excellent properties are closely related to dislocation movements, which depend on the stacking fault energies (SFEs). In CSAs, SFEs show large fluctuations due to variations in the local atomic environments in the vicinity of the stacking faults. In this work, first-principle calculations were performed to investigate the origin of the fluctuations in the SFEs of the widely studied CSA, NiCoCr, which show a very wide distribution from about −200 mJ/m2 to 60 mJ/m2. Compared to the common understanding that only atoms in close proximity to the stacking fault influence the SFEs in pure metals and dilute alloys, charge redistribution can be observed in several nearby planes of the stacking fault in NiCoCr, indicating that atoms several atomic layers away from stacking fault also contribute to the SFEs. Our analysis shows that Cr plays a major role in the large fluctuation in the SFEs of NiCoCr based on both electronic and magnetic responses. The flexible electronic structure of Cr facilitates easier charge transfer with Cr in several nearby atomic planes near the stacking fault, leading to significant changes in the d-electron number, orbital occupation number, and magnetic moments of Cr.

Anisotropic materials with abnormal Poisson's ratios and acoustic velocities.

Isotropic materials are required to adhere to various mechanical principles due to their limited thermal stability. For instance, it is essential for Poisson's ratio to be within the range of -1 to 0.5, and the longitudinal wave velocity must exceed the transverse wave velocity. Nevertheless, perfect crystals, as anisotropic materials, have the ability to defy conventional rules. Through the integration of high-throughput processes and first-principles calculations, a comprehensive exploration of known materials was conducted, resulting in the establishment of a database featuring an extreme anisotropic mechanism. This included the identification of abnormal Poisson's ratios (with the directional Poisson's ratio ranging from -3.00 to 3.67), the discovery of extreme negative linear compressibility, the determination of the upper and lower limits of the sound velocity, and other associated properties. Several materials with abnormal Poisson's ratios (<-1 or >0.5) were listed, and their peculiar mechanical behavior, wherein the volume decreased counterintuitively with uniaxial tension, was discussed. Finally, this study focused on the velocities of longitudinal and transverse waves, with specific emphasis on materials exhibiting transverse wave velocities that exceeded the longitudinal wave velocities.

Tunable electronic, transport, and optical properties of fluorine- and hydrogen-passivated two-dimensional Ga2O3 by uniaxial strain

Two-dimensional (2D) semiconductors have shown great prospects for future-oriented optoelectronic applications, whereas the applications of conventional 2D materials are significantly impeded by their low electron mobility (⩽200 cm2 V−1 s−1). In this work, strain-mediated fluorine- and hydrogen-passivated 2D Ga2O3 systems (FGa2O3H) have been explored via using first-principles calculations with the Heyd–Scuseria–Ernzerh and Perdew–Burke–Ernzerhof functionals. Our results reveal a considerable high electron mobility of FGa2O3H up to 4863.05 cm2 V−1 s−1 as the uniaxial tensile strain reaches 6%, which can be attributed to the enhanced overlapping of wave functions and bonding features. Overall, when applying uniaxial strain monotonously along the a(b) direction from compressive to tensile cases, the bandgaps of 2D FGa2O3H increase initially and then decrease, which originates from the changes of σ* anti-bonding in the conduction band minimum and π bonding states in the valence band maximum accompanying the lengthening Ga–O bonds. Additionally, when the tensile strain is larger than 8%, the stronger π bonding at the G point leads to an indirect-to-direct transition. Besides the highest electron mobility observed in n-type doped 2D FGa2O3H with 6% tensile strain, the electrical conductivity is enhanced and further elevated as the temperature increases from 300 K to 800 K. The variations of the absorption coefficient in the ultraviolet region are negligible with increasing tensile strain from 0% to 6%, which sheds light on its applications in high-power optoelectronic devices.

Stacking-dependent interlayer magnetic interactions in CrSe2.

Recently, CrSe2, a new ferromagnetic van der Waals two-dimensional material, was discovered to be highly stable under ambient conditions, making it an attractive candidate for fundamental research and potential device applications. Here, we study the interlayer interactions of bilayer CrSe2using first-principles calculations. We demonstrate that the interlayer interaction depends on the stacking structure. The AA and AB stackings exhibit antiferromagnetic (AFM) interlayer interactions, while the AC stacking exhibits ferromagnetic (FM) interlayer interaction. Furthermore, the interlayer interaction can be further tuned by tensile strain and charge doping. Specifically, under large tensile strain, most stacking structures exhibit FM interlayer interactions. Conversely, under heavy electron doping, all stacking structures exhibit AFM interlayer interactions. These findings are useful for designing spintronic devices based on CrSe2.

Assembly-inspired multiferroicity with nontrivial Chern insulating phase from exohedral metallofullerenes.

Fullerene-assembled low-dimensional materials have been experimentally realized in polymorphic forms and have attracted significant interest very recently. Here, we predict a two-dimensional (2D) honeycomb lattice material TM2(C60)3 (TM = Cr, Mo, and W) assembled from exohedral metallofullerene clusters TM(C60)3 that could exhibit planar triangular geometries. According to first-principles calculations combined with Monte Carlo simulations, we suggest that these 2D assembled materials exhibit various exotic physical properties, including ferromagnetism, ferroelectricity, and quantum anomalous Hall effect. Interestingly, mechanical strains could effectively tune their magnetic moments and switch the conducting spin channel of the Dirac bands at the Fermi level. Our work provides a new cluster-assembly design strategy toward cluster-assembled 2D materials based on fullerene characters.

The type-I, III nodal ring, type-I, III quadratic nodal point, and Dirac valley phonons in 2D kagome lattices M2C3 (M = As, Bi, Cd, Hg, P, Sb, Zn)

Topological phases in kagome systems have garnered considerable interest since the introduction of the colloidal kagome lattice. Our study employs first-principle calculations and symmetry analysis to predict the existence of ideal type-I, III nodal rings (NRs), type-I, III quadratic nodal points (QNPs), and Dirac valley phonons (DVPs) in a collection of two-dimensional (2D) kagome lattices M2C3 (M = As, Bi, Cd, Hg, P, Sb, Zn). Specifically, the Dirac valley points (DVPs) can be observed at two inequivalent valleys with Berry phases of +π and −π , connected by edge arcs along the zigzag and armchair directions. Additionally, the QNP is pinned at the Γ point, and two edge states emerge from its projections. Notably, these kagome lattices also exhibit ideal type-I and III nodal rings protected by time inversion and spatial inversion symmetries. Our work examines the various categories of nodal points and nodal ring phonons within the 2D kagome systems and presents a selection of ideal candidates for investigating topological phonons in bosonic systems.