Phonon Dispersion Analysis Research Articles

Investigating the potential of triclinic ABSe3 (A = Li, Na, K, Rb, Cs; B = Si, Ge, Sn) perovskites as a new class of lead-free photovoltaic materials

In recent years, chalcogenide perovskites have emerged as promising candidates with favorable structural, electrical, and optical properties for photovoltaic applications. This paper explores the structural, electronic, and optical characteristics of ABSe3 perovskites (where A = Li, Na, K, Rb, Cs; B = Si, Ge, Sn) in their triclinic crystallographic phases using density functional theory. The stability of these materials is ensured by calculating formation energies, tolerance factors (Tf), and phonon dispersion. The Eform values of all ABSe3 are negative, suggesting favorable thermodynamic stability. The Tf values range between 0.82 and 1.1, which is consistent with stable perovskites. The phonon dispersion analysis of the chalcogenide perovskites revealed no imaginary frequencies in any of the vibrational modes, confirming their stability. The electronic band structures and corresponding density of states are computed to unveil the semiconducting nature of the studied compounds. These perovskites are promising for high-performance solar cells due to their indirect bandgaps (Eg, 1.10–2.33 eV) and a small difference between these indirect and direct gaps (0.149–0.493 eV). The Eg values increase as the ionic radii of A-site elements increase (Li < Na < K < Rb < Cs). At the B-site, Si-based chalcogenides have the largest Eg values, followed by Sn-based and then Ge-based materials. Furthermore, optical properties such as the real part and imaginary part of the dielectric function, refractive index extinction coefficient, optical conductivity, absorption coefficient, reflectivity, and energy loss are predicted within the energy range of 0–50 eV. Several ABSe3 materials, particularly LiGeSe3 and NaGeSe3, demonstrated optical properties comparable to both traditional and emerging materials, suggesting their potential for effective use in solar cells.

Realization of hydrogenation-induced superconductivity in two-dimensional Ti2N MXene.

Two-dimensional (2D) MXene superconductors have been currently attracting considerable interest due to their unique electronic properties and diverse applicability. Utilizing first-principles computational methods, we have designed two distinct configurations of hydrogenated 2D Ti2N MXene materials, namely Ti2NH2 and Ti2NH4, and have conducted an exhaustive analysis of their structural stability, electronic characteristics, and superconductivity. Hydrogenation endows monolayer Ti2N with inherent metallic characteristics, as evidenced by an elevated density of states (DOS) at the Fermi level (Ef). Notably, Ti2NH4 exhibits a superconducting critical temperature (Tc) of 15.8 K, which is predominantly ascribed to the electronic contributions stemming from the Ti 3d orbitals. Analysis of phonon dispersion underscores the pivotal role that diverse lattice vibrational modes play in electron-phonon coupling (EPC), particularly the significance of low-frequency vibrations for facilitating electron pairing and the emergence of superconductivity. Furthermore, strain engineering can effectively modulate the superconducting properties of Ti2NH4, with a 2% tensile strain enhancing the EPC strength (λ) to 0.857 and increasing Tc to 18.7 K. This research elucidates the superconducting mechanisms of hydrogenated Ti2N structures, offering valuable insights for the development of novel 2D superconducting materials.

2D bilayer chromium pnictogens as a metallic material under DFT investigation through their structural, vibrational, electronic, and elastic properties

A comprehensive investigation of the structural, vibrational, electronic, and elastic characteristics of four hexagonal bilayer chromium pnictogens (CrX; X = N, P, As, Sb) materials has been conducted using first-principles calculations based on density functional theory (DFT). The phonon dispersion investigations demonstrate the dynamic stability of the examined hexagonal bilayers belonging to pnictogens group, in their planar structure. According to our phonon dispersion analysis, only two materials, CrN/CrN and CrP/CrP, are found to be dynamically stable, while the other two, CrAs/CrAs and CrSb/CrSb are reveal to be dynamically unstable. The band structure calculations carried out utilizing HSE06 hybrid functionals reveals the metallic nature of bilayer chromium pnictogens. In all CrX materials, the highest work function we observed for CrN/CrN material as 5.17 eV. Along the armchair direction in CrN/CrN compounds, highest elastic constants (C2D) is obtained among all CrX compounds, measured as 192.47 Nm−1 for electron carriers. In addition to examining the phonon dispersion, we also assessed their mechanical stability by the computation of elastic characteristics. Our calculated elastic parameters and polar diagrams of Young's modulus and Poisson's ratio indicate the mechanical stability of all the systems under consideration. To further our understanding of CrX compounds, we also acquired data on their deformation potential for electron carriers in both armchair and zigzag orientations. This work unequivocally demonstrates the advantages of CrX bilayers as potential materials for upcoming robust conducting devices and also possible applications for a 2D metallic material.

A novel and promising Penta-Octa-Based silicon carbide semiconductor

Penta-octa-graphene (POG) consists of pentagonal and octagonal carbon rings, hosting type-I and type-II Dirac line nodes due to its sp2 and sp3 mixed bonds. Inorganic analogs of 2D carbon lattices have increased the potential applications and changed the main properties of carbon-based structures. Therefore, this work proposes penta-octa-graphene based on silicon carbide using DFT simulations. With a cohesive energy of −5.22 eV/atom, POG-Si5C4 is energetically viable in comparison with other silicon carbide-based monolayers. Phonon dispersion analysis confirms the POG-Si5C4 dynamical stability. MD simulations demonstrate that this new monolayer can withstand temperatures up to 1020 K. Electronic analysis indicates it is a semiconductor with an indirect band gap transition of 2.02 eV. The mechanical properties exhibit anisotropy, with Young’s modulus ranging from 38.65 to 99.47 N/m and an unusual negative Poisson’s ratio of −0.09. The band edge alignment suggests that POG-Si5C4 holds potential for hydrogen generation through photocatalytic water splitting. This research opens possibilities for designing inorganic penta-octa-based structures and provides insights for future experimental and theoretical studies focused on exploring and optimizing advanced silicon-carbide 2D materials.

Investigating stress-induced effects on the multifaceted properties of cubic NaTaO3 perovskite oxide: prospects for advanced applications

This study explored the structural, optoelectronic, elastic, mechanical, and thermodynamic behaviour of NaTaO3 cubic perovskite oxide, under varying stress levels. Geometric property analysis reveals a decrease in lattice constants from 4.1 Å to 3.7 Å and cell volume from 71.1–53.4 Å3 as stress increases from 0 to 100 GPa. X-ray diffraction analysis indicated the stable cubic phase with slight peak shifts, demonstrating the material's structural flexibility. Electronic properties revealed an initial increase in the band gap (1.698 eV to 1.936 eV) with applied stress up to 60 GPa, which could be attributed to complex interactions within the material's electronic structure. Optical property analysis suggested that NaTaO3 possessed high optical absorption and conductivity, along with low reflectivity. Furthermore, elastic constants meeting the Born-stability condition (C11 – C12 > 0, C11 + 2C12 > 0, and C44 > 0) confirm the material's mechanical stability. Additional characteristics like the Poisson ratio, Cauchy pressure, and Frantsevich ratio highlighted the ductile and anisotropic nature of NaTaO3. Thermodynamic and phonon dispersion analysis suggested that NaTaO3 can withstand high-stress levels, evidenced by its elevated Debye temperature, indicating superior mechanical stability and increased resistance to thermal degradation. Based on these findings, NaTaO3 proposed as a potential candidate for photovoltaic and thermoelectric devices.

Graphsene as a novel porous two-dimensional carbon material for enhanced oxygen reduction electrocatalysis

Graphene allotropes with varied carbon configurations have attracted significant attention for their unique properties and chemical activities. This study introduces a novel two-dimensional carbon-based material, termed Graphsene (GrS), through theoretical study. Comprising tetra-, penta-, and dodeca-carbon rings, GrS’s cohesive energy calculations demonstrate its superior structural stability over existing graphene allotropes, including graphyne and graphdiyne families. Phonon dispersion analysis confirms GrS’s dynamic stability and its relatively low thermal conductivity. All calculated GrS elastic constants meet the Born criteria, ensuring mechanical stability. Ab-initio molecular dynamic simulations show GrS maintains its structure at 300 K. HSE06 calculations reveal a narrow electronic bandgap of 20 meV, with the electronic band structure featuring a highly anisotropic Dirac-like cone due to its intrinsic structural anisotropy along armchair and zigzag directions. Notably, GrS is predicted to offer exceptional catalytic performance for the oxygen reduction reaction, favoring the four-electron reduction pathway with high selectivity under both acidic and alkaline conditions. This discovery opens promising avenues for developing metal-free catalyst materials in clean energy production.

DFT based study of copper calcium halide perovskite nanomaterials for optoelectronic and energy applications

The mechanical, electronic, optical, and thermoelectric analyses of CuCaX3 (X = Cl, Br, I) have been done using DFT based TB-mBJ approach. The stability of CuCaX3 (X = Cl, Br, I) has been confirmed from the enthalpy of formation; values for CuCaCl3, CuCaBr3, and CuCaI3 are −1.07 eV, −1.55 eV, and −2.15 eV, respectively. The phonon spectra plot is also discussed, and the phonon dispersion analysis confirms that the CuCaX3 systems are dynamically stable since no imaginary modes are observed. The modified Becke-Johnson exchange potential is used to evaluate the opto-electronic and thermo-electric properties. By replacing anions (Cl to I), the band gap of the studied material in the visible region has been tailored, from 2.9 eV to 2.65 eV, for renewable energy devices. In addition, various optical properties such as dielectric constant, refraction, absorption, optical conductivity, and optical loss factor have been analyzed for optoelectronic applications. With the replacement of anions (Cl to I), the peaks of maximum intensities shifted to lower energy to values of 7.2 eV, 6.2 eV and 5 eV for CuCaCl3, CuCaBr3 and CuCaI3 respectively. Furthermore, the BoltzTrap code has been used to discuss thermal conductivity, power factor, Hall coefficient, specific capacitance and electron densities in detail for thermoelectric applications. The CuCaX3 family of perovskites has been found to have bandgaps falling in the visible region for light-emitting diodes (LEDs). These also exhibit high thermal efficiency, making them potential multifunctional candidates for optoelectronic and energy harvesting applications.

First principle studies on structural, electronic, elastic, optical, and thermoelectric properties of XGeCl3 (X = Rb/Cs): Promising compounds for green energy application

AbstractThis study employed density functional theory (DFT) embedded in Wien2K code to evaluate the physical features of the XGeCl3 (X = Rb/Cs) cubic halide perovskites. The structural optimization has been performed considering generalized gradient approximation (GGA) and electronic properties have been computed considering modified Becke‐Johnson potential (mBJ). The formation energy and phonon dispersion analysis establish the stability of the investigated compounds. Mechanical stability is further confirmed by the computed diverse elastic coefficients. It has been discovered that the examined substances are naturally ductile. The refractive index, reflectivity, and absorption coefficient, are among the optical parameters that have been estimated and analyzed. Interesting results have been obtained for the transport properties of XGeCl3 (X = Rb/Cs). The XGeCl3 (X = Rb/Cs) exhibits a high Seebeck coefficient (X = Rb/Cs) and the largest figure of merit (about 0.99), indicating significant potential for thermoelectric applications.

Transferable machine learning interatomic potential for carbon hydrogen systems.

In this study, we developed a machine learning interatomic potential based on artificial neural networks (ANN) to model carbon-hydrogen (C-H) systems. The ANN potential was trained on a dataset of C-H clusters obtained through density functional theory (DFT) calculations. Through comprehensive evaluations against DFT results, including predictions of geometries and formation energies across 0D-3D systems comprising C and C-H, as well as modeling various chemical processes, the ANN potential demonstrated exceptional accuracy and transferability. Its capability to accurately predict lattice dynamics, crucial for stability assessment in crystal structure prediction, was also verified through phonon dispersion analysis. Notably, its accuracy and computational efficiency in calculating force constants facilitated the exploration of complex energy landscapes, leading to the discovery of a novel C polymorph. These results underscore the robustness and versatility of the ANN potential, highlighting its efficacy in advancing computational materials science by conducting precise atomistic simulations on a wide range of C-H materials.

Large piezoelectric responses and ultra-high carrier mobility in Janus HfGeZ3H (Z = N, P, As) monolayers: a first-principles study.

Breaking structural symmetry in two-dimensional layered Janus materials can result in enhanced new phenomena and create additional degrees of piezoelectric responses. In this study, we theoretically design a series of Janus monolayers HfGeZ3H (Z = N, P, As) and investigate their structural characteristics, crystal stability, piezoelectric responses, electronic features, and carrier mobility using first-principles calculations. Phonon dispersion analysis confirms that HfGeZ3H monolayers are dynamically stable and their mechanical stability is also confirmed through the Born-Huang criteria. It is demonstrated that while HfGeN3H is a semiconductor with a large bandgap of 3.50 eV, HfGeP3H and HfGeAs3H monolayers have narrower bandgaps being 1.07 and 0.92 eV, respectively. When the spin-orbit coupling is included, large spin-splitting energy is found in the electronic bands of HfGeZ3H. Janus HfGeZ3H monolayers can be treated as piezoelectric semiconductors with the coexistence of both in-plane and out-of-plane piezoelectric responses. In particular, HfGeZ3H monolayers exhibit ultra-high electron mobilities up to 6.40 × 103 cm2 V-1 s-1 (HfGeAs3H), indicating that they have potential for various applications in nanoelectronics.

The effect of Li doping on superconductivity of SiH4(H2)2 from first-principles calculations

From first-principles calculations, we calculated the crystal structure, electronic properties, and phonon properties of SiH4(H2)2 and LiSiH4(H2)2 at 180 GPa, respectively. The electronic properties of SiH4(H2)2 and LiSiH4(H2)2 were studied by analyzing the band structure, density of states (DOS), charge density and Mulliken population. The results show that both substances are metals. However, the lower N(Ef) of SiH4(H2)2 indicates that the Cc structure behaves in a weak metal nature at 180 GPa. Moreover, after Li atom doping, significantly improved the H atoms near the Fermi surface states density (from 0.04 to 0.34 states/eV). And when the pressure reaches 350 GPa, the DOS of H is as high as 1.02 states/eV. This leads to a higher Tc. And the analysis of phonon dispersion and phonon state density (PDOS) shows that the dynamic stability of LiSiH4(H2)2 is better. By comparing the electronic and phonon properties of SiH4(H2)2 and LiSiH4(H2)2, we can find that the superconductivity of SiH4(H2)2 can be improved by doping Li atoms to a certain extent.

Discovery of 2D Materials using Transformer Network‐Based Generative Design

Two‐dimensional (2D) materials offer great potential in various fields like superconductivity, quantum systems, and topological materials. However, designing them systematically remains challenging due to the limited pool of fewer than 100 experimentally synthesized 2D materials. Recent advancements in deep learning, data mining, and density functional theory (DFT) calculations have paved the way for exploring new 2D material candidates. Herein, a generative material design pipeline known as the material transformer generator (MTG) is proposed. MTG leverages two distinct 2D material composition generators, both trained using self‐learning neural language models rooted in transformers, with and without transfer learning. These models generate numerous potential 2D compositions, which are plugged into established templates for known 2D materials to predict their crystal structures. To ensure stability, DFT computations assess their thermodynamic stability based on energy‐above‐hull and formation energy metrics. MTG has found four new DFT‐validated stable 2D materials: NiCl4, IrSBr, CuBr3, and CoBrCl, all with zero energy‐above‐hull values that indicate thermodynamic stability. Additionally, GaBrO and NbBrCl3 are found with energy‐above‐hull values below 0.05 eV. CuBr3 and GaBrO exhibit dynamic stability, confirmed by phonon dispersion analysis. In summary, the MTG pipeline shows significant potential for discovering new 2D and functional materials.

Elastic, Optical, and Thermoelectric Properties of 2D Square Lattice and Hexagonal Zinc Chalcogenides under First‐Principles Calculations

Herein, elastic, optical, and thermoelectric properties of zinc chalcogenides with 2D square lattice and hexagonal phases [s‐ and h‐ZnX (X = GrVI)] are reported. The s‐ZnX and h‐ZnX structures are achieved to be dynamically stable, according to the phonon dispersion studies. All s‐ and h‐ZnX compounds are found to be semiconductor, with direct and indirect bandgaps ranging from 0.81 to 2.77 eV under PBE and 1.70 to 4.15 eV by HSE06 calculations. The effective mass, mobility, and relaxation time of electron and hole carriers in the band structures of s‐ and h‐ZnX are investigated to gain a better insight of these materials. In addition to the phonon dispersion analysis, their mechanical stability in terms of elastic properties is evaluated, and the resulting elastic parameters validate their mechanical stability. The optical properties of s‐ and h‐ZnX are inspected in the occurrence of field polarizations across parallel and perpendicular directions. At room temperature, s‐ZnTe compound has an optimum figure of merit (ZT) value, indicating it as the superlative thermoelectric material in the entire series. These compounds may also be explored in ultraviolet lasers, solar cells, electronic image displays, high‐density optical memory, photodetectors, and solid‐state laser devices.

Structural, vibrational, electronic, and elastic properties of 2D alkali carbide as a metallic material

We have investigated the structural, vibrational, electronic, and elastic properties of two-dimensional alkali carbide, viz. X2C (X = Li, Na, K, Rb) materials. Using the projector augmented wave (PAW) approach within the generalized gradient approximation, the X2C structure has been carefully explored. The X2C compounds are found to be dynamically and energetically stable, according to phonon dispersion studies. After performing both PBE and HSE06 functionals calculations on all X2C compounds, it was confirmed that they all exhibit a metallic bandgap. For Na2C material, we found the highest work function as 6.09 eV in entire alkali carbide materials series. The largest elastic constants (C2D) for Li2C was found in entire series of X2C compounds, with a value of 29.27 Nm−1 in the armchair direction for both the carriers. In addition to the phonon dispersion analysis, we have evaluated their mechanical stability in terms of elastic properties, and the resulting elastic parameters and polar diagrams of Young's modulus and Poisson's ratio validate their mechanical stability. The good metallicity and hardness of 2D X2C might suggest its potential application as hard conductor.

First principles study on structural, vibrational, electronic and elastic properties of 2D alkaline-earth carbides as a metallic material

A detailed first principle investigation of two-dimensional alkaline-earth carbides (M2C; M = Mg, Ca, Sr, Ba) materials is reported for the first time. The M2C structure has been thoroughly investigated using the projector augmented wave (PAW) method under the generalized gradient approximation (GGA) framework of density functional theory (DFT). The M2C compounds are found to be dynamically and energetically stable, according to phonon dispersion studies. The electronic properties of M2C materials provided the essence of band structure and projected density of states of these compounds. Under the investigation of Perdew–Burke–Ernzerhof (PBE) functional, M2C compounds are found to exhibit metallic behavior. In the series of M2C compounds, with an exception of Ba2C compound, remaining appears to be narrow gap semiconducting materials under Heyd-Scuseria-Ernzerhof (HSE06) functional study. Mg2C compund shows the highest work function in the series as 4.47 eV. In addition to the phonon dispersion analysis, we have evaluated their mechanical stability in terms of elastic properties, and the resulting elastic parameters and polar diagrams of Young's modulus and Poisson's ratio validate their mechanical stability. The good metallicity and hardness of 2D M2C compounds might suggest their potential applications as hard conductors.

Thermodynamic measurements and ab initio calculations of the indium-lithium system

The limiting enthalpy of the solution of liquid indium in liquid tin was measured at 723 K. The calorimetric method was applied to determine the standard enthalpy of the formation of intermetallic phases and alloys from the In-Li system. The measurements were done at 747 K and 756 K. The structures of prepared alloys were confirmed by the X-ray diffraction measurements. Besides that, the ab initio calculations allowed the modeling of the formation energies, the volume thermal expansion, the heat capacity under constant pressure, and the elastic properties of the intermetallic phases. The theoretical formation energies show good agreement with the experimental findings. The analysis of the phonon dispersion indicates an instability of the InLi phase in the Fd-3m space group. A further investigation on the atomic arrangement in the case of the equiatomic ratio is suggested.

First-principles investigation on structural and optoelectronic properties of buckled SnO monolayer for effective solar energy scavenging

Two-dimensional (2D) materials have gathered considerable attention for next-generation optoelectronic devices owing to their intriguing optical and electronic properties. The semiconductor SnO has shown potential for flexible electronics, optoelectronics, gas sensing, and Li-ion battery applications due to its indirect bandgap, and high carrier mobility. In the present work, we investigate the physical properties of a buckled tin oxide (SnO) monolayer using density functional theory (DFT) calculations. The structural analysis reveals that buckled SnO monolayer is energetically stable and exhibits the hexagonal crystal structure. Phonon dispersion analysis depicts the dynamical stability of the buckled SnO monolayer and obtained the quadratic behavior of flexural acoustic modes (ZA) near the zone center. Further, the electronic property calculation shows that the buckled SnO is an indirect semiconductor with a bandgap of 1.71 eV and the transparent behavior of the material is disclosed by analyzing the optical parameters. Moreover, the computed solar power conversion efficiency of 16.76% for buckled SnO monolayer demonstrates the potential as a light absorber in the field of solar energy scavenging.

First-principles calculations to investigate structural, elastic, electronic, and thermoelectric properties of monolayer and bulk beryllium chalcogenides

A detailed first-principles investigation on the structural, vibrational, elastic, electronic, and thermoelectric properties of the family of beryllium chalcogenides (BeX; X = O, S, Se, Te) in hexagonal monolayer (h-BeX) and bulk (zinc blende; zb-BeX) phases are studied in this work. The stabilities of the compounds are assessed by phonon dispersion analysis and elastic properties. The band structure and partial density of states predicts the nature and understanding of the electronic properties of the considered BeX compounds. The effective mass, mobility and relaxation time for carriers are also predicted for both the BeX phases. The thermoelectric properties are evaluated for a wide temperature range of 50–800 K in terms of thermal conductivity (κ), electrical conductivity (σ), Seebeck coefficient (S) and figure of merit (ZT). The considered BeX materials shows outstanding thermoelectrical promises. The present findings will undoubtedly aid experimentalists in prospective synthesis and future thermoelectric power applications of the recognized BeX compounds.

The Stability and Electronic and Thermal Transport Properties of New Tl‐Based MAX‐Phase Compound Ta2TlX (X: C or N)

Herein, a comprehensive computational investigation of the stability and mechanical, electronic, and thermal transport properties of two new Tl‐based MAX‐phase compounds Ta2TlC and Ta2TlN is presented. The negative values of the formation energy ensure the chemical stability of the materials. Moreover, the analysis of phonon dispersion and elastic constants shows that the compounds are dynamically and mechanically stable. From the electronic structures, the miss of bandgap at the Fermi level reveals the metallic nature of the compounds, and state densities indicate the difference between the conductivities of the two compounds. Furthermore, interestingly low thermal conductivities are obtained for both compounds. Finally, the ambition is that this report will inspire new theoretical and experimental studies on these compounds.

Mechanism of Co atom point defects on different termination surfaces of WC–Co/diamond interface by first-principles

Based on the density functional theory, the first-principles method had been used to calculate the binding energy, the charge density of the interface, Mulliken population, density of states, band structure and phonon dispersion analysis of Co atom point defects on the W-terminated surface and C-terminated surface of the WC–Co/Diamond film-base interface. The results showed that the binding energy of W-GD, W-VD, W-SD sites on the W termination surface with WC–Co/Diamond interface was gradually weakened. And the binding energy of C-GD, C-SD, C-VD sites on the C termination surface was the same as the former. From the charge density, Co atom on the W-terminated surface of WC(100) had a stronger influence on the film-base interface than the C-terminated surface. From the analysis of the Mulliken population, the ability of Co to transfer charge on W-terminated surface was stronger than C-terminated surface. According to the density of states analysis, the Fermi level state density of the W terminal surface was higher than that of the C terminal surface and the activity of the W terminal surface was higher than that of the C terminal surface. Through the analysis of the electronic energy band structure, the system indicated significant metallicity. The phonon spectrum showed that the presence of Co atoms on the W-terminated surface and C-terminated surface of the WC–Co/Diamond film-base interface is stable.