First-principles Study Research Articles

Location preference of boron and nitrogen dopants at graphene/copper interface

Controlling the placement of dopants can significantly tailor graphene's properties, but this process is influenced by copper substrates during vapor deposition. Understanding the influence of interfacial atomic structures on the preference for dopant locations is crucial. In this work, we conducted a systematic first-principles study of boron- and nitrogen-doped graphene on copper {111}, considering both sublattice and superlattice configurations. Our calculations revealed that the formation energy is minimized at the top-fccb site (−0.60 eV) for boron and the hcp-fcca site (1.94 eV) for nitrogen, suggesting a possible selective distribution of dopants in both sublattice and superlattice arrangements at the graphene/copper interface. Furthermore, a lower formation energy indicates a higher release of energy during doping, resulting in a stronger interfacial binding. Since formation energy is closely associated with out-of-plane interactions, while in-plane interactions remain relatively stable, these differences offer potential avenues for modifying dopant distribution at graphene/copper interfaces.

Oxygen-doping induced tunable optoelectronic properties of two-dimensional (2D) 1T-MgF2 monolayer: A first-principles study

Here, we studied the physical properties of atomic oxygen-doped two-dimensional (2D) MgF2 monolayer using density functional theory. The undoped MgF2 exhibits an insulating behavior. However, it shows a small amount of incident light absorption in the visible region when an F-atom is substitutional doped with an oxygen (O) atom. Further, the increasing oxygen concentration shows an enhanced optical absorption of light in the visible spectrum. Hence, it can be used as an absorption band pass/stop filter. The absorption spectrum is consistent with the calculated extinction coefficient. The increased absorption shows the improved conductivity of doped MgF2. Moreover, the dielectric constant and refractive index increase with increasing O-doping concentration. Its refractive index enhances more than that of silicon (3.9). The increased O-doping also enhances the reflection of light in the microwave to the infrared region, which is justified by the transmission spectrum. The energy losses also increase with increasing O-concentration. These losses show the existence of plasma resonances. The dielectric and optical responses show that it behaves like a high-k dielectric material for large O-doping concentrations. The discussion above indicates that the O-doped 2D MgF2 monolayer is an excellent electronic and dielectric material for electronic, optical, and optoelectronic applications.

First-principles study of the effect of Dirac phonons on the thermoelectric properties in monolayer Ge2H2

The Dirac phonons have been widely attention due to their unique edge or surface states. However, research on their influence in the realm of thermoelectric transport in semiconductor materials remains limited. Here, we have systematically investigated the geometric structure, stability, electronic, thermal conductivity, and thermoelectric properties of the monolayer Ge2H2 and Ge2 based on density functional theory and the Boltzmann transport equation (BTE). The phonon spectrum of monolayer Ge2H2 exhibits both Hourglass-type and Dirac-type phonon dispersion curves. The band structure of monolayer Ge2H2 reveals a relatively large band gap of 1.02 eV (1.75 eV for HSE), indicating that it is a direct band gap semiconductor. These two features make monolayer Ge2H2 an ideal material for exploring the effect of Dirac phonons on thermoelectric transport properties. In this paper, we determined that the lattice thermal conductivity (κl) in Ge2H2 is 0.59 Wm−1K−1 at 300 K, but undergoes a sharp increase upon removal of H atoms. This is mainly attributed to the disappearance of the Dirac phonons and the change of lattice vibration modes by removing the H atoms. While also exhibiting high carrier mobilities (134.86 cm2/Vs for holes) and extended scattering time (4.22 × 10−14 s for holes), indicative of excellent thermoelectric performance. With increasing temperature, the ZTmax of p-type doping reaches 0.63 at 700 K in Ge2H2. Remarkably, at 300K, the Hourglass-type phonon contributes only 5.94 % to κl, while the Dirac phonon contributes 3.44 %. Further analysis reveals that the Dirac phonon within Hourglass-type in monolayer Ge2H2 contributes 2.5 % to the ZTmax at 300K. Our investigation elucidates the impact of Dirac phonons on thermoelectric properties, providing valuable insights for future design and exploration of high-ZT thermoelectric materials.

Investigation of Piezoelectric Properties of Wurtzite AlN Films under In-Plane Strain: A First-Principles Study

This research article presents a comprehensive first-principles study on the piezoelectric properties of Wurtzite Aluminum Nitride (AlN) films under in-plane strain conditions. By calculating the piezoelectric tensor coefficients (e33, e31, and e15), we investigate the variation patterns of these constants with respect to in-plane strain. Our results indicate significant changes in the piezoelectric constants within the range of in-plane strain considered, exhibiting a linear trend despite opposite trends for e33 compared to e31 and e15. This study highlights the extreme sensitivity of AlN films’ piezoelectric performance to in-plane strain, suggesting its potential as an effective means for tuning and optimizing the piezoelectric properties of AlN-based devices.

Exploring defect engineering in monolayer TiS[formula omitted] for next-generation electronic devices: Insights from first-principles study

Titanium trisulfide monolayer (TiS3) is a quasi-1D crystal with promising applications in a range of fields, including photoelectrochemical cells and thermoelectrics. Despite the emerging importance of monolayer TiS3, little is known regarding its intrinsic defects. In this work, we systematically investigate the stability, electronic, and magnetic properties of native defects in single layer TiS3, using Density Functional Theory. We consider S and Ti monovacancies, divacancies, extended Ti-nS (n=2−8) vacancy complexes, S and Ti antisites, as well as their complexes. We show that the likelihood of the formation of sulfur vacancies is strongly dependent on the symmetrically inequivalent lattice site at which the S vacancy is located. Under S-rich conditions, single sulfur vacancies are shown to be energetically more favorable than divacancies. In contrast, under Ti-rich conditions sulfur divacancies are more favorable than single S vacancies. We show that STi and TiS1 are most likely to form under S-rich and Ti-rich conditions, respectively, with low formation energies of -10.42 eV and -9.18 eV, and are therefore likely to be prevalent in single layer TiS3. We further consider defect levels in the band-gap, and show that several of these intrinsic defects are potential n-type or p-type dopants, while others will form deep electron/hole traps. Further, we show that while a number of these intrinsic defects induce no spin in the host, most intrinsic defects will induce a net magnetic moment in the host. The commonality of these defects in TiS3, will significantly impact applications such as spintronics, thermoelectrics, and the manufacturing of electronic devices.

HeF2 and ArF2 molecules from first-principles study

HeF2 and ArF2 molecules from first-principles study

Effect of strain on thermoelectric properties of 2D SiH monolayer for solar cell and renewable energy applications: A First-Principles study

The structural, electrical, optical, and thermal characteristics of SiH monolayer were assessed using first-principles based calculations. The SiH monolayer is a semiconductor by nature and we found that the energy band gap remains zero by applying (-10%, -5%, -2%, 0%, 2%5%, 10%) different orders of strain into this material. The optical characteristics of SiH are examined for photon energies between 0 and 10 eV and electrical, thermal, Seebeck coefficient, and power factor against temperature (300˚ K 800˚ K) is reported. SiH monolayer has theoretical power conversion efficiencies up to 20%. SiH monolayer under consideration is appropriate for photovoltaic and optoelectronic applications, according to their electrical, optical, and thermoelectric characteristics.

Investigating electrocatalytic properties of β12-borophene as a cathode material for an efficient lithium-oxygen battery: a first-principles study

Responding to the pressing need to mitigate climate change effects due to fossil fuel consumption, there is a collective push to transition towards renewable and clean energy sources. However, the effectiveness of this move depends on an efficient energy storage system that surpasses current lithium-ion battery technology. The lithium-oxygen battery, having significantly high theoretical specific capacity compared to other systems, has emerged as a promising solution. However, the issues of poor cathode electrode conductivity and slow kinetics during discharge product formation have limited its practical applications. In this work, the first principles-based density functional theory was used to investigate the electrocatalytic properties of β12-borophene as a cathode electrode material for a high-performance lithium-oxygen battery. The adsorption energy, charge density distributions, Gibbs free energy changes, and diffusion energy barriers of lithium superoxide (LiO2) on β12-borophene were calculated. Our findings revealed several important insights: The adsorption energy was found to be − 3.70 eV, suggesting a strong tendency for the LiO2 to remain anchored to the material during the discharging process. The dynamics in the charge density distributions between LiO2 and the β12-borophene substrate exhibited complex behavior. The analysis of the Gibbs free energy changes of the reactions yielded an overpotential of − 1.87 V, this moderate value suggests spontaneous reactions during the formation of the discharge products. Most interestingly, the density of states and band structure analysis suggested the preservation of metallic properties and improved electrical conductivity of the material after the adsorption of LiO2. Additionally, β12-borophene has a relatively low diffusion energy barrier of 1.08 eV, implying effortless diffusion of the LiO2 and an increase in the rate of discharging process. Ultimately, the predicted electronic properties of β12-borophene, make it a strong candidate as a cathode electrode material for an efficient lithium-oxygen battery.

First-principles study of electronic and magnetic properties of Fe atoms on Cu2N/Cu(100)

Abstract First-principles calculations were conducted to investigate the structural, electronic, and magnetic properties of single Fe atoms and Fe dimers on Cu2N/Cu(100). Upon adsorption of an Fe atom onto Cu2N/Cu(100), robust Fe–N bonds form, resulting in the incorporation of both single Fe atoms and Fe dimers within the surface Cu2N layer. The partial occupancy of Fe-3d orbitals lead to large spin moments on the Fe atoms. Interestingly, both single Fe atoms and Fe dimers exhibit in-plane magnetic anisotropy, with the magnetic anisotropy energy (MAE) of an Fe dimer exceeding twice that of a single Fe atom. This magnetic anisotropy can be attributed to the predominant contribution of the component along the x direction of the spin–orbital coupling Hamiltonian. Additionally, the formation of Fe–Cu dimers may further boost the magnetic anisotropy, as the energy levels of the Fe-3d orbitals are remarkably influenced by the presence of Cu atoms. Our study manifests the significance of uncovering the origin of magnetic anisotropy in engineering the magnetic properties of magnetic nanostructures.

First-principles studies on the oxygen vacancy formation in α-Na2FePO4F and β-Na2FePO4F

The orthorhombic β-Na2FePO4F has been extensively studied, however, a novel monoclinic α-Na2FePO4F has not been explored sufficiently. Oxygen vacancies (VO) can affect the physical and chemical properties of materials, and oxygen vacancy formation energy reflects the difficulty of VO formation. Using first-principles methods, we have calculated the formation energies of VO and their relevant charge states in both α-Na2FePO4F and β-Na2FePO4F. Our results reveal that charged vacancies (VO+1 or VO+2) are easier to form than neutral vacancies (VO0). The reduction of the Fermi level, the decrease in the oxygen partial pressure, or the increase of the temperature are found to decrease the formation energy of VO. The formation energy of VO in α-Na2FePO4F is slightly lower than that in β-Na2FePO4F. The electronic density of states of α-Na2FePO4F and β-Na2FePO4F suggest that more defect states are introduced into the band gap as the charge states increase. These defect states are mainly the 3d orbitals of the Fe atoms. The introduction of oxygen vacancies distorts the [FeO4F2] octahedra, which affect the charge density distribution and the defect states introduced in the band gap. Significantly, oxygen vacancies have a local impact on the charge density redistribution in both α-Na2FePO4F and β-Na2FePO4F. These findings provide theoretical insights into the formation of oxygen vacancies and the control of oxygen release.

First-Principles Study on the Role of Cu and Cl-Based Dopants in NiO

First-Principles Study on the Role of Cu and Cl-Based Dopants in NiO

From MAX to MXene: A case study of Sc2TlC MAX phase, Sc2C pristine MXene, and surface-functionalized Sc2CT2 (T=O, F) MXenes

The MXenes-based two-dimensional (2D) materials have become a hotspot of recent research due to their exciting physical behavior. In this first-principles study, we investigate the Sc2TlC MAX phase and its 2D derivatives, focusing on the transformation of Sc2TlC into a Sc2C 2D sheet and the subsequent surface functionalization of Sc2C with oxygen (O) and fluorine (F). Investigations of the electronic structures reveal that the Sc2TlC MAX phase is metallic and nonmagnetic, while the conversion to the Sc2C pristine monolayer and surface functionalized Sc2CO2 induces significant changes in its electronic structure but retains its metallic behavior. On the other hand, functionalization of the Sc2C monolayer with F2 (such as Sc2CF2) evolves semiconductor-like behavior with an energy gap of magnitude 1.325 eV for the up-spin state and 1.227 eV for the down-spin state. The optimal optical absorption of ultraviolet (UV) for Sc2TlC MAX phase and Sc2C, Sc2CO2, and Sc2CF2 MXenes have been found as 13.8 × 105 cm−1, 49.17 × 104 cm−1, 81.39 × 104 cm−1, and 69. ×104 cm−1, respectively. Investigations of the optical properties reveal considerable reflection and absorption capabilities, particularly upon exposure to low-energy light photons, suggesting their potential for optoelectronic and energy harvesting applications.

First-principles study of stability, order and disorder based on an entropy descriptor in noble and ferromagnetic transition metal alloys

Binary alloys AB composed of ferromagnetic metals A (Fe, Co, Ni) and the late 4d−5d noble metals B (Rh, Pd, Ag, Ir, Pt, Au) have been investigated using density functional theory with the generalized gradient approximation to understand the role of magnetism in the stability and the order–disorder transition which has an impact on their physicochemical properties, their applications and their possible implementation as precursors of high-entropy alloys. The enthalpy of formation related to the stability demonstrates that all the alloys are more stable in the ferromagnetic phase than in the nonmagnetic phase. The transition from ordered to disordered phases is quantified using a descriptor which is the standard deviation of the energy spectrum of a set of small nanoalloys with random atomic configurations. The study highlights the fact that the entropy-related descriptor, which is a quantity in determining the formation of a disordered phase as a solid solution or an ordered phase is highly dependent on the atomic environment. Despite the fact that the overall variation of this descriptor is supposed to be unpredictable, there is a noticeable trend showing that the environment-dependent ferromagnetism contributes to a chemical order in alloys and nanoalloys and that this order depends on the atomic radius of the species considered. The results indicate that species with small atomic radii, such as nickel, rhodium or iridium are more likely to form solid solutions than species with larger atomic radii and with more delocalized orbitals.

First-principles study on the electronic structure and photocatalytic properties of novel two-dimensional Janus CrXCN4 (X = Si, Ge)

Abundant studies demonstrate the significant role of Janus-structured two dimensional semiconductors as photocatalytic materials, highlighting their substantial advantages and importance in photocatalysis. In this work, CrXCN4 (X = Si, Ge) Janus monolayers were constructed based on CrC2N4, and the thermal stability, thermodynamic stability, mechanical stability, electronic properties, and optical properties of the monolayers were systematically investigated. Furthermore, an investigation was conducted to examine the impact of biaxial strain on their electronic and light absorption properties. The findings reveal that both monolayers exhibit direct band gap characteristics, with high absorption coefficients for visible light owing to their appropriate band gaps (1.44 eV for CrSiCN4 and 1.15 eV for CrGeCN4, respectively). At compressive strains exceeding 3%, the CrSiCN4 monolayer demonstrates an optimal band edge position, suggesting its potential as a photocatalyst for overall water splitting. Furthermore, as the compressive strain increases, the absorption spectra have blue-shifted and the absorption coefficient becomes higher, exceeding 2 × 105 cm−1 under a −3% compressive strain. Our study highlights the potential applications of CrXCN4 monolayers in the field of optoelectronic device, particularly emphasizing the promising candidacy of CrSiCN4 as an efficient photocatalyst.

Effect of Pb-site doping on the structure, electronic and mechanical properties of CsPbI3 perovskite: A first-principles study

CsPbI3 has received a great deal of attention as the light-harvesting component of pure inorganic perovskite solar cells (PSCs). It is revealed that Pb-site doping is an effective way to enhance the electrical and optical properties of CsPbI3 compared with other methods. In this study, within the framework of the density functional theory (DFT), first-principles method was used to investigate different Pb-site ionic doping effect on the structural, mechanical, electrical, and optical properties of CsPbI3. We considered totally 11 doping elements, each with a doping concentration of 12.5 % (denoted as CsPb0.875M0.125I3, M is the doping element). The results revealed that all the doping systems are structurally stable with decreased bandgap values compared with the pristine CsPbI3. CsPb0.875M0.125I3 (M=Ge, Sn) exhibits similar behavior to CsPbI3, while CsPb0.875M0.125I3 (M= As, Sb, Bi) series present electron-doping character and CsPb0.875M0.125I3 (M=Ga, In, Tl) shows hole-doping effect. Mechanically, all the other elements mono-doped CsPbI3 satisfy the stability requirement except CsPb0.875Ga0.125I3. Moreover, most of doping systems show enhanced the absorption strength in the visible light region. By synthetically considering the mechanical, electronic and optical properties, it is suggested that CsPb0.875M0.125I3 (M=Sb, Fe) exhibit relatively superior characteristics compared with pristine and other elements mono-doped CsPbI3. Results obtained in the present work may provide valuable guidance for the synthesis and the performance refinement of all-inorganic CsPbI3-based PSCs in the future.

Structural evolution and mechanical response of multiple Al Σ5(210) grain boundaries with segregation of solute atoms: First-principles study

Grain boundary (GB) segregation of solute atoms is a key factor affecting the microstructure and macroscopic properties of materials. In this study, first-principles calculations were carried out to investigate the effect of solute atoms (Mg and Cu) segregation on the structural evolution and mechanical response of Al ground-state Σ5(210) GB (GB-Ⅰ) and metastable Σ5(210) GBs (GB-Ⅱ and GB-Ⅲ). The GB energy, segregation energy, and the theoretical tensile strength of the multiple Σ5(210) GBs were calculated. The results show that both Mg and Cu atoms tend to segregate in the boundary plane, thus reducing GB energy and improving GB stability. The segregation of Cu atoms reduced the GB energy more significantly than that of Mg atoms. The segregation of solute atoms can change the symmetric GB structure into an asymmetric one or induce GB phase transformation. The theoretical strength of GB-I is weaker than that of the metastable GB-II with higher GB energy, suggesting that grain boundaries with higher energy are not necessarily unstable. In addition, the effect of solute atom segregation on the GB strength depends not only on the type of element but also on the specific GB structure. The weakening effect of Mg segregation in GB-I and GB-II is due to the weak MgAl bond which enlarges the low charge density region of GB and increases the free volume of GB. The strengthening of GB-I and GB-II by Cu segregation mainly depends on the stronger AlCu bond than AlAl bond along the GB fracture path. The enhanced strength of GB-III with Mg and Cu segregation is attributed to the GB structural phase transformation caused by the segregation of solute atoms. The calculation results further elucidate the relationship between element segregation and grain boundary characteristics.

Janus MoSH/WSi2N4 van der Waals Heterostructure: Two-Dimensional Metal/Semiconductor Contact.

Constructing heterostructures from already synthesized two-dimensional materials is of significant importance. We performed a first-principles study to investigate the electronic properties and interfacial characteristics of Janus MoSH/WSi2N4 van der Waals heterostructure (vdWH) contacts. We demonstrate that the p-type Schottky formed by MoSH/WSi2N4 and MoHS/WSi2N4 has extremely low Schottky barrier heights (SBHs). Due to its excellent charge injection efficiency, Janus MoSH may be regarded as an effective metal contact for WSi2N4 semiconductors. Furthermore, the interfacial characteristics and electronic structure of Janus MoSH/WSi2N4 vdWHs can not only reduce/eliminate SBH, but also forms the transition from p-ShC to n-ShC type and from Schottky contact (ShC) to Ohmic contact (OhC) through the layer spacing and electric field. Our results can offer a fresh method for optoelectronic applications based on metal/semiconductor Janus MoSH/WSi2N4 vdW heterostructures, which have strong potential in optoelectronic applications.

[formula omitted] magnetism engineering in the low-buckled hexagonal SiS monolayer: A first-principles study

In this work, vacancy- and doped-induced magnetism engineering is investigated to functionalize the non-magnetic low-buckled hexagonal silicon sulfide (SiS) monolayer. This monolayer is an indirect gap semiconductor two-dimensional (2D) material with an energy gap of 2.20(3.02) eV obtained from the PBE(HSE06)-based calculations. Creating a single Si vacancy leads to a significant magnetization of SiS monolayer with the feature-rich half-metallic nature. Herein, a total magnetic moment of 1.89 μB is obtained and magnetic properties are produced mainly by S and Si atoms closest to the defect site. In contrast, single S vacancy preserves the non-magnetic nature inducing a band gap reduction of the order of 26.36%. n-type doping with P atom metalizes the monolayer, meanwhile As impurity leads to the emergence of the half-metallicity with a total magnetic moment of 1.00 μB. Similarly, this value is also obtained by p-doping using P and As atoms as dopants, where the diluted magnetic semiconductor nature is obtained. Moreover, doping with IA- (Na and K) and IIIA-group (Al and Ga) atoms is also proposed to engineer the magnetism in SiS monolayer. It is found that these impurities induce either half-metallic or diluted magnetic semiconductor behaviors with total magnetic moment between 0.99 and 1.00 μB. The electronic and magnetic properties are regulated mainly by the interactions between impurities and their neighbor S atoms, which modify the charge distribution in their outermost orbitals. In addition, the Bader charge analysis asserts that dopant atoms gain charge from the host monolayer when substituting S atom, meanwhile they act as charge loser — transferring charge to the host monolayer when doping at Si sublattice. The presented results may suggest efficient approaches to properly engineer SiS monolayer electronic and magnetic properties, making new 2D candidates for spintronic applications.

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.