First-principles Study Research Articles

Twist angle-driven photoreduction of carbon dioxide on bilayer black phosphorus – A first-principles study

Utilizing first principles calculations, the product selectivity in photocatalytic CO2 reduction was modulated by manipulating the twisted angle in bilayer black phosphorus. Four twisted angles, 0° (AA stacking), 15.40°, 19.00° and 24.66°, were constructed. Comprehensive investigations revealed enhanced carrier mobility and lifetime, especially at a 24.66° twist. Furthermore, an in-depth analysis of the CO2 reduction processes in these four systems was undertaken. Our simulations indicate that in the AA stacking, the photocatalytic CO2 reduction yields multiple products, including HCHO, CH3OH, and CH4, demonstrating limited product selectivity. However, when the surface is twisted at 15.40°, 19.00°, or 24.66°, the sole product is CH4. Remarkably, the 24.66° configuration exhibits the lowest energy barrier for the rate-determining step, measuring just 1.29 eV. These observations suggest that by carefully adjusting the twisted angle in bilayer black phosphorus, we can significantly improve both the activity and selectivity of CO2 photoreduction.

Pressure dependence of superconducting behavior of solid Br and I: A first-principles study

Based on the first-principles calculations, this study employs the HSE06 functional for the first time to understand the high-pressure behavior of diatomic molecular crystal bromine and iodine. It meticulously replicates the metallization process of iodine and bromine from aspects including bond length, charge density, band structure, and density of states. Furthermore, we also investigate the pressure-dependent superconducting properties of monoatomic phases of bromine and iodine, probing into the reasons behind the discrepancies in Tc values among different phases.

Biaxial strain modulation of NO2 adsorption on χ3 borophene: A first-principles study

Based on first-principles calculations, the effects of applying biaxial strain to χ3 borophene and the adsorption behavior of NO2 molecule on the surface of χ3 borophene under strain are investigated. Firstly, the pristine borophene exhibits a metallic electronic structure and the thermodynamic stability of χ3 borophene is demonstrated by molecular dynamics simulations. Different adsorption sites and orientations are selected on the χ3 surface, and the optimal adsorption is found to be the S2 conformation, which has an adsorption energy of −1.589 eV. The applied biaxial strain significantly alters the electron density distribution of the χ3 borophene surface, which is predicted to be able to achieve a modification of the adsorption properties for NO2. Finally, we investigate the NO2 adsorption behavior of χ3 borophene surfaces under 1% to 5% biaxial tensile and compressive strains. Biaxial strain is found to enhance the NO2 adsorption capacity of the χ3 borophene surface, and χ3 at 3% biaxial tensile strain has the highest adsorption energy. Therefore, these results show that χ3 borophene can be a candidate material for gas sensors and theoretically guide researchers to develop more effective sensor materials for gas sensing.

Influence of the optoelectronic properties of F-MoTe2 systems under the combined action of an external electric field and biaxial tensile-compressive deformation: a first-principles study

The effects of an applied electric field on the electronic structure, charge transfer, and optical characteristics of molybdenum telluride (MoTe2) systems doped with halogen F atoms during biaxial tensile-compressive deformation were explored using first-principles approaches. The results show that the MoTe2 system exhibits an upward shift of the Fermi energy level and a downward shift of the conduction band when crossing the Fermi energy level due to the doping of halogen F atoms. Subsequently, we applied an electric field of −0.4 eV∼−0.4 eV to the F-MoTe2 system. The change of the F-MoTe2 system under the electric field effect is very small. This result indicates that the F-MoTe2 system can be stabilized in this range. Subsequently, we chose to apply a biaxial tensile-compressive deformation of −14%−14% to the F-MoTe2 system under the action of an electric field of +0.4 eV. The F-MoTe2 system underwent a transition from a semiconductor to a metal, with an increase in the carrier concentration and a good shift in electrical conductivity. The compressive strain gives better results than the tensile strain. In terms of optical characteristics, the absorption and emission peaks of the F-MoTe2 system are blueshifted under the combined effect of electric field and stress.

Regulating coordination environment around transition metal (Fe, Co) single atom catalysts for efficient Hg0 adsorption

Elemental mercury (Hg0) is one of the main pollutants released during coal combustion, which is difficult to remove due to its hydrophobicity and volatility, resulting in serious environmental pollution. Therefore, it is urgent to develop a low-cost and high-performance catalyst to remove Hg0. In this work, using first-principles study, the effect of nonmetal (NM = B, C and O) coordination environment on the charge distribution of graphene-supported transition metal single atom catalysts (TM-N4-SAC) has been investigated. It is found that regulating the TM-N4-SAC with NM coordination atoms with fewer valence electrons than N atom can cause TM atoms to lose more electrons, and the charge distribution in the active center to be locally deviated. Moreover, in-depth analysis of the adsorption configuration, charge density difference, charge transfer, adsorption energy and density of state of Hg0 adsorption on NM modified TM-N4-SAC confirmed that the adsorption of Hg0 can be effectively enhanced only when TM atoms lose more electrons. Thus, Fe-N3B- and Co-N3B-SAC have the strongest ability to adsorb Hg0 because they have the most negative adsorption energy of −1.13 and −0.49 eV. This work provides theoretical guidance for the design of SAC for efficient adsorption of Hg0.

Atomic-scale insights into the electrochemical mechanisms of aluminum-sulfur batteries: A first-principles study of Al-S clusters on graphene

Aluminum-sulfur (Al-S) batteries, known for their high energy density, cost-effectiveness, and sustainability, face challenges due to limited understanding of their atomic-level electrochemical mechanisms. This study uses first-principles calculations to explore the geometric and electronic structures of Al-S clusters and their interaction with graphene substrates. Key findings include charge transfer from graphene to Al-S clusters, especially in C@Al2S6 and C@Al2S3, and moderate adsorption strength crucial for reversible cycling. Thermodynamic analysis identifies the free energy change in the transition from C@Al2S6 to C@Al2S3, while AIMD simulations confirm structural stability, providing insights for optimizing Al-S battery performance.

Effect of V-VIB group ternary elements on the properties of Ti2AlM-type O-phases: A first-principles study

Understanding the underlying constitutional mechanisms for the stability of complex phases and comprehending it is crucial to find new materials with desired mechanical and physical properties. In TiAl-alloys with ternary alloying additions orthorhombic phases can form but the effects of different alloying elements on their stability and other properties are only scarcely known. We present a comprehensive study using density functional theory (DFT) within the generalized gradient approximation (GGA) with the Perdew–Burke–Ernzerhof (PBE) method to determine energetic, and mechanical stability criteria and evaluate the electronic densities of states (DOS) and band structures to understand bonding behavior. The stability of Ti2AlM, as a bulk O-phase in ternary TiAl-based systems is predicted by investigating VB (V, Nb, and Ta) and VIB (Mo, W) group elements as ternary addition M. The electronic density of states and band structure indicate that the ternary elements addition causes charge redistribution through the formation of a bond, which significantly alters the stability and mechanical properties. All investigated compounds exhibit negative formation energies and the calculated elastic constants reveal that all are mechanically stable. For the different O-phase types investigated Ti2AlMo is the most stable and Ti2AlV the least stable when comparing energies of formation. The obtained elastic moduli and Pugh's ratios support the idea that Ti2AlM (M = V, Nb, Ta, Mo, and W) O-phases have attractive mechanical characteristics and exhibit ductility. Among all the systems investigated, Ti2AlMo, and Ti2AlW provide the highest increase in B, G, and E values. Based on the elastic constants also indicators for the mechanical properties, such as Poisson's ratio (ν), and Pugh ratio G/B, are calculated. According to our calculations, the brittle Ti2AlV is harder than the ductile Ti2AlMo. Based on the results of the present study, the Ti2AlM type O-phase is considered a promising constituent for designing new materials in the ternary Ti–Al-M system.

Activation of efficient hydrogen evolution on 1T-VS2 nanoribbons by low-cost transition metals: A first-principles study

Electrocatalytic water splitting is a very important energy conversion technology that utilizes renewable energy sources to produce hydrogen for sustainable energy development. In this work, the catalytic performance of 1T-VS2 (1T phase of vanadium disulfide) nanoribbons in the hydrogen evolution reaction (HER) was investigated based on first-principles calculations. It was found that 1T-VS2 nanoribbons have a Gibbs free energy (ΔGH*) of 0.05 eV, demonstrating its excellent HER performance. Moreover, some transition metal substitutions can further improve this performance (e.g. the ΔGH* of the Ti/Fe-1T-VS2 are as low as −0.02/0.04 eV). The mechanism of the performance enhancement is thoroughly investigated. The improved catalytic performance of HER is mainly promoted by hybridization between the V-d and TM-d-orbitals. The crystal orbital Hamiltonian population (COHP) and integral crystal orbital Hamiltonian habitation (ICOHP) calculations show that the HER properties are closely related to the filling of bonding and antibonding states. The differential charge density indicates that the adsorption of H results in an effective charge transfer at the interface and an increase in the conductivity, leading to an increase in the HER. The HER activity of the TM-1T-VS2 (TM stands for transition metal) nanoribbons is also related to the proximity of the adsorption site to the edge. Our work suggests that the TM-1T-VS2 nanoribbons are expected to be low cost and highly efficient catalysts.

First-principles study on the microstructure, band structure, mechanical and optical properties of AB-stacked bilayer graphene under constant neutron irradiation with different electric field magnitudes and directions

Carbon-based devices have superior performance and lower power consumption compared to silicon-based devices. However, graphene and related two-dimensional materials are easily influenced by radiation due to their extremely high surface-to-volume ratio. Under constant neutron irradiation conditions, there have been no studies on the effects of the magnitude and direction of an external electric field on various properties of the AB system. This study systematically investigated the neutron irradiation effects on the AB system and the influence of the different electric fields on the properties of the AB system under constant irradiation conditions using the density functional theory and ab initio molecular dynamics method that assigns energy to the primary knock-on atom. The results indicate that under constant neutron irradiation with different electric fields, the changes in system configuration dominate the influence on band structure, while the impact of surface ripples is relatively limited. Reducing the interlayer spacing of the system can make the configuration more stable, which makes the band structure under the electric field more stable. The primary factors influencing the Young's modulus (Y) of the system are changes in the microstructure and the appearance of surface ripples, while the influence of system configuration is relatively limited. Under the irradiation conditions, the electric field can to some extent accurately modulate the band gap of the system. However, it will also correspondingly reduce the system's Y to a certain extent, causing negative impacts on the electrical and thermal conductivity.

First-principles study of phase-dependent carrier transport mechanism for MASnI3 Sn-based halide perovskite

Organic-inorganic hybrid perovskites have attracted tremendous attentions owing to their excellent properties as next-generation photovoltaic devices. With soft covalent framework, organic-inorganic hybrid perovskites exhibit different phases at different temperatures. The band-edge features of perovskites are mainly contributed by inorganic framework, which means the structural differences between these phases would lead to complex carrier transport. We investigated the carrier transport of Sn-based organic-inorganic hybrid perovskite CH3NH3SnI3 (MASnI3), considering acoustic deformation potential scattering, ionized impurity scattering, and polar optical phonon scattering. It is found that the electron mobility of each phase of MASnI3 is strongly correlated with the Sn–I–Sn bond angle and there is in-plane/out-of-plane anisotropy. The projected crystal orbital Hamilton population analysis suggested that the tilt and rotation of the [SnI6]4− octahedron influence the Sn(p)–I(p) orbital electron coupling and the electron transport, leading to different band-edge features in multiple phases. The carrier mobility with respect to temperature was further calculated for each phase of MASnI3 in respective temperature intervals, showing lower carrier mobility in high temperature. Comparing the contribution of different scattering mechanisms, it was found that the dominant scattering mechanism is polar optical phonon scattering, while multiple scattering mechanisms compete in individual cases.

First-principles study on the differences in mechanical and optoelectronic properties between monolayer graphene and AA bilayer graphene after neutron irradiation

Two-dimensional materials are easily affected by radiation. So far, there is no work to predict the neutron irradiation effects of AA bilayer graphene. Furthermore, the differences and comparisons of various properties between monolayer graphene and AA bilayer graphene after irradiation in the approximately same neutron environment have not been reported. In this study, the neutron irradiation processes on monolayer graphene and AA bilayer graphene were simulated in ab initio molecular dynamics. The mechanical, and optoelectronic properties of monolayer and AA bilayer systems before and after irradiation were calculated using the method based on density functional theory. The results indicate that the AA bilayer system is more resistant to neutron irradiation than the monolayer system. The bandgap of the monolayer (bilayer) system after irradiation will reach the order of 0.1 eV. This article has important value in exploring the methods of radiation reinforcement technology for carbon-based devices.

Design of Single-Atom Catalysts on C5N2 for Nitrogen Fixation at Ambient Conditions: A First-Principles Study.

Single atom catalysts (SACs) exhibit the flexible coordination structure of the active site and high utilization of active atoms, making them promising candidates for nitrogen reduction reaction (NRR) under ambient conditions. By the aid of first-principles calculations based on DFT, we have systematically explored the NRR catalytic behavior of thirteen 4d- and 5d-transition metal atoms anchored on 2D porous graphite carbon nitride C N . With high selectivity and outstanding activity, Zr, Nb, Mo, Ta, W and Re-doped C N are identified as potential nominees for NRR. Particularly, Mo@C N possesses an impressive low limiting potential of -0.39 V (corresponding to a very low temperature and atmospheric pressure), featuring the potential determining step involving *N-N transitions to *N-NH via the distal path. The catalytic performance of TM@C N can be well characterized by the adsorption strength of intermediate *N H. Moreover, there exists a volcanic relationship between the catalytic property U and the structure descriptor , which validates the robustness and universality of , combined with our previous study. This work sheds light on the design of SACs with eminent NRR performance.

Prediction of a rippled and auxetic two-dimensional Sn9C15 layers with tunable electronic band structure: A first-principle study

We predicted a two-dimensional Sn9C15 monolayer with regular ripple using first-principles methods by utilizing the VASP code based on density functional theory (DFT). The rippled Sn9C15 monolayer is an indirect bandgap semiconductor with anisotropic mechanical properties (Poisson’s ratio and Young’s modulus). It exhibits auxetic properties with a negative Poisson’s ratio (NPR) of up to −0.58 and exceptional flexibility in the x direction. Furthermore, its bandgap can be adjusted from 1.16 eV to 0.68 eV with a strain in the x direction of less than 12 %. The rippled Sn9C15 monolayer is sensitive to polarized light and has a broad absorption spectrum from infrared to ultraviolet. In addition, the bilayer rippled Sn9C15 exhibits a regularly arranged nanotube-like structure and is a stable direct bandgap semiconductor material. These findings enrich the emerging landscape of 2D rippled monolayers and suggest potential applications in diverse fields such as optics, nanomechanics, electronic devices, and filtration.

Exploring the structural, electronic, and optical properties of novel two-dimensional ABX-type materials

A first-principles study of the structural, electrical, and optical properties of graphene-like two-dimensional (2D) materials ABX (A=Na/K, B=C/Si/Ge, and X=N/P/As) such as NaCN, KCN, NaCP, KCP, etc was undertaken using state-of-the-art Density Functional Theory (DFT). The investigation encompasses essential parameters such as structural stability through ab initio molecular dynamics (AIMD), electronic structure, and dielectric constants. The AIMD measurements reveal that the structures stay stable for up to 10 picoseconds (ps). Band structure calculations at the PBE level of theory revealed that most materials are semi-conducting with a band gap of 1-3 eV, except NaCN and KCN, which exhibited insulating behaviour. Using hybrid functional (HSE), only eight materials were identified to have a band gap in the visible range. Optical properties have also been investigated to understand their interaction with light. Peaks in the imaginary component of the dielectric function were attributed to inter-band transitions. Several materials were discovered to be optimal for photo-catalysis, while six were found to exhibit conductivity of the order of ∼1012 (Ω−1cm−1s−1) at room temperature.

A First-Principles Study on the Reaction Mechanisms of Electrochemical CO2 Reduction to C1 and C2 Products on Cu(110)

The mechanism of the electrochemical CO2 reduction reaction on a Cu(110) surface has yet to be fully revealed. In this work, based on first-principles calculations, we investigate the mechanisms of the CO2 reduction reaction to produce C1 (including one C atom) and C2 (including two C atoms) products on a Cu(110) surface. The results show that CH4 and C2H5OH are the main C1 and C2 products on the Cu(110) surface, respectively. CH4 is produced along the pathway CO2 → COOH* → CO* → CHO* → CH2O* → CH3O* → CH4. C2H5OH is produced via the C-C coupling pathway between CO* and CH2O* intermediates, which is the key reaction step. This is because CO* and CH2O* coupling to CO-CH2O* has the lowest barrier among the CHxO* (x = 0–2) coupling pathways. Therefore, it is the most likely C-C coupling pathway. Further, CO-CH2O* is gradually hydrogenated to C2H5OH along the following pathway: CO-CH2O* → CHO-CH2O* → CHOH-CH2* → CH2OH-CH2* → CH2OH-CH3* → C2H5OH.

Synthesis, characterization, and evaluation of improved electrochemical performance of vanadium and zinc co-doped Ni-rich oxide cathode materials: experimental and first-principles study

Synthesis, characterization, and evaluation of improved electrochemical performance of vanadium and zinc co-doped Ni-rich oxide cathode materials: experimental and first-principles study

Exploring potential of lead-free KSn0.5Ge0.5I3 based perovskite solar cell: A combined first-principle DFT and SCAPS-1D study

Perovskite solar cells present a promising alternative to conventional silicon or lead-based solar cells, offering a synergistic blend of cost-effectiveness and potential for elevated power conversion efficiency. We investigated the potential of an innovative KSn0.5Ge0.5I3-based perovskite solar cell (PSC) using density functional theory (DFT) and SCAPS-1D simulation studies. Computational analysis via DFT probed the crystal structure, elastic, mechanical, and optoelectronic properties of KSn0.5Ge0.5I3. Tolerance factor computation (0.94) and negative formation energy (-3.16 eV) affirmed the thermodynamic stability of the orthorhombic phase in KSn0.5Ge0.5I3. Optical variables including refractive index, absorption coefficient, dielectric function, optical loss, and reflectivity, were computed to explore KSn0.5Ge0.5I3 viability in PV applications. Band structure analysis, density of states (DOS), and projected density of states (PDOS) have been used to determine the band gap (∼1.87 eV), effective masses, and mobility of e-/h+. We have conducted SCAPS-1D simulation for diverse PSCs configurations using various holes transport layers (HTLs) and electron transport layers (ETLs), identified IGZO (Eg = 3.05 eV) as a proficient ETL while CuSbS2 (Eg = 1.58 eV) as an effective HTL. A comprehensive investigation of parameters such as absorber layer thickness, shunt and series resistance, donor and acceptor density, absorber defect density, back contact metal, temperature, and interface characteristics was undertaken, and the impact on PV device performances was assessed through current-voltage (IV) and quantum efficiency (Q.E) characteristics curves. These findings underscore the potential of KSn0.5Ge0.5I3 as a promising material for PSCs, offering a sustainable and eco-friendly avenue for future renewable energy.

Theoretical study of electronic structures, magnetic properties, and ultrafast spin manipulation in transition metal adsorbed polycyclic-aromatic-hydrocarbon molecules.

We present a first-principles study of the structural, electronic, and magnetic properties of TM(PAH)0/+ (TM = Fe, Co, Ni; PAH = C10H8, C16H10, C24H12, C32H14) complexes and explore the laser-induced spin dynamics as well as their stability with respect to various laser parameters. For each complex, the most stable configuration shows that the TM atom prefers to adsorb at the hollow site of the carbon ring with a slight deviation from the center. The electronic structure and spin localization of the complexes are found to be largely affected by the TM type. Driven by various laser pulses, spin-crossover scenarios are achieved in all structures, while spin-transfer between TM and PAH is achieved in Ni(C10H8), Ni(C16H10), and Ni(C24H12). The influence of the laser energy and chirp on the dynamics is also investigated, providing important information regarding the stability and sensitivity of the dynamical process. All results are believed to reveal the physics nature of the TM-PAH systems, to guide the experimental realization of their ultrafast spin dynamics and thus to promote their applications in future spintronics.

The electronic, magnetic, and optical behaviors of graphyne modulated by metal atoms adsorption: a first-principles study

The electronic, magnetic, and optical behaviors of graphyne modulated by various adsorbed metal atoms (Li, Na, K, Mg, Ca, Al, and Zn) from typical metal-ion batteries are studied by first-principles calculation. Notably, Mg and Zn adsorption systems are deemed unstable. In contrast, Li, Na, K, Ca, and Al systems exhibit two preferential adsorption sites, with the optimal position being the hollow center site within the large acetylenic ring. Upon the adsorption of these metal atoms, except for Ca adsorption systems exhibit semi-metallic behavior, while the other metal adsorption systems induced a transition from p-type to n-type semiconductors with decreased band gaps. Intriguingly, the inherent magnetism of the metal atoms vanished, resulting in a total magnetic moment of 0 μ B for the adsorption systems. Furthermore, the optical absorption and reflectivity peak positions for Ca adsorption systems show a significant redshift from violet to green and blue light regions. Conversely, other adsorption systems exhibit new absorption and reflection peaks in the infrared range, accompanied by an increase in both absorption coefficient and reflectivity across various spectral regions. These findings are conducive to the application in the field of novel optoelectronics and optical films.

Factors influencing charge transport at perovskite–charge transport layer interfaces: current strategies, challenges, and perspectives based on first-principles studies

Charge transport at the interface between a perovskite absorbing layer and the charge transport layer (CTL) has a major role in determining perovskite solar cell device efficiency and long-term stability. Hence, a detailed operando characterization of the factors influencing charge transport at perovskite/CTL interfaces needs to be discussed. This perspective summarizes recent studies involving charge transport through perovskite and CTL interfaces. An overview is provided of the recent advances in the fundamental understanding of how these interfaces influence device performance. Based on recently reported articles, some of the crucial factors such as energy-level alignment, defects, and non-radiative recombination are identified. The identification is made from an atomistic point of view as these factors have a strong influence on charge transport at perovskite/CTL interfaces. Furthermore, we share our perspective on calculating said factors influencing interfacial charge transport from different approaches using density functional theory (DFT) and beyond.