Pseudopotential Approach Research Articles

First-principles analysis of the structural, thermodynamic, elastic and thermoelectric properties of LuXCo2Sb2 (X = V, Nb and Ta) double half Heusler alloys

We used the pseudopotential plane wave approach, as implemented in the Quantum Espresso program, to investigate the impact of X atoms (V, Nb, and Ta) on the physical properties of LuXCo2Sb2 double half Heusler alloys. We determined the equilibrium structural parameters, including the crystal lattice parameters, atomic position coordinates, and bulk modulus, with and without including the spin-orbit effects. The predicted single-crystal elastic constants (Cij) show that the title compounds are mechanically stable with a pronounced elastic anisotropy. The bulk modulus, shear modulus, Young's modulus, Poisson coefficient, Debye temperature, and Vickers hardness coefficient were deduced from Cij via the Voigt-Reuss-Hill approximations. We also determined the variations of some macroscopic physical parameters as functions of temperature and pressure, namely the thermal expansion coefficient, lattice thermal conductivity, heat capacity at constant volume, Debye temperature and entropy. The considered alloys demonstrate special thermal properties under pressure and heat conditions, specifically, their low thermal expansion coefficient and lattice thermal conductivity; their thermal expansion coefficient is lower than 4.5 × 10−5 K−1 at 1000 K, and lattice thermal conductivity don’t exceed 1 W.m−1 K−1 for temperatures higher than 300 K. Furthermore, we investigated the temperature and charge carrier concentration dependencies of some thermoelectric coefficients. The results of this study reveal the potential of the considered compounds for achieving a figure of merit greater than 0.5 at a temperature of 500 K and a doping concentration of 1020 cm−3.

B-doping on the electronic structure and photocatalytic properties of g-C3N4/Janus PtSSe heterojunctions: A first-principles study

The effect of B doping on the stability, electronic structure, work function, and optical properties of g-C3N4/Janus PtSSe heterojunctions has been investigated based on the density-functional theory plane-wave ultrasoft pseudopotential approach. It is shown that the binding energy of g-C3N4/PtSSe after B doping is negative and has a low layer spacing and lattice mismatch rate. It is stable at a room temperature of 300 K, proving its structural and thermodynamic stability. B-atom doping of g-C3N4/SPtSe and g-C3N4/SePtS heterojunctions leads to the upward shift of the Fermi energy level resulting in a significant reduction of the band gap and significant orbital hybridization. The impurity band near the Fermi energy level easily transfers electrons from the valence band into the conduction band, which makes electron leaps easier. Different built-in electric fields are formed when the g-C3N4 and Se(S) atomic layers are in contact. The reduction of the bandgap after B doping enables the photogenerated electron-hole pairs between the heterojunction interfaces to be better separated under the action of the built-in electric field, which reduces the composite rate of the electron-hole pairs and greatly improves the carrier migration and photocatalytic performance. The absorption and reflection coefficients of g-C3N4/SPtSe-BNC and g-C3N4/SePtS-BNC are the highest and decrease slowly in the visible region, which indicates that they have the optimal photocatalytic performance, and they can effectively broaden the range of light absorption and promote the utilization of light. The introduction of the B–B bonding effectively improves the photocatalytic activity of the heterojunction.

Large amplitude dust-acoustic solitary waves and double layers in nonthermal warm complex plasmas

Using a Sagdeev pseudo-potential approach, where the nonlinear structures are stationary in a comoving frame, the arbitrary or large amplitude dust-acoustic solitary waves and double layers have been studied in dusty plasmas containing warm positively charged dust and nonthermal distributed electrons and ions. Depending on the values of the critical Mach number, which varies with the plasma parameter, both supersonic and subsonic dust-acoustic solitary waves are found. It is found that our plasma system under consideration supports both positive and negative supersonic solitary waves and only positive subsonic solitary waves and negative double layers. The parametric regimes for the existence of subsonic and supersonic dust-acoustic waves and how the polarity of solitary waves changes with plasma parameters are shown. It is observed that the solitary wave and double layer solutions exist at the values of Mach number around its critical Mach number. The basic properties (amplitude, width, speed, etc.) of the solitary pulses and double layers are significantly modified by the plasma parameters (viz., ion to positive dust number density ratio, ion to electron temperature ratio, nonthermal parameter, and positive dust temperature to ion temperature ratio). The applications of our present work in space environments (viz., cometary tails, Earth’s mesosphere, and Jupiter’s magnetosphere) and laboratory devices, where nonthermal ion and electron species along with positively charged dust species have been observed, are briefly discussed.

Electron beam driven ion-acoustic solitary waves in plasmas with two kappa-distributed electrons

Formation and the basic features of arbitrary amplitude ion-acoustic solitary waves (IASWs) in a plasma consisting of warm positive ions, two kappa-distributed electrons and an electron beam are investigated by using the Sagdeev pseudopotential approach. It is shown that the soliton existence domain (Mach number limits) sensitively depends on temperature of ions, spectral index of cool electrons and concentration of hot electron species while spectral index of hot electrons, hot-to-cool electron temperature ratio and also concentration of electron beam do not considerably affect this domain. It is also found that temperature of electron beam only affect the existence domain of rarefactive solitons. Furthermore, it is shown that considered plasma medium supports the coexistence of positive and negative IASWs. Moreover, effect of different plasma parameters such as hot-to-cool electron density ratio, ion-to-cool electron temperature ratio, beam-to-ion density ratio, hot-to-cool electron temperature ratio and superthermality index of electron species on the basic features of positive and negative IASWs is investigated numerically. Finally, the effect of plasma parameters on the parametric regime of coexistence of compressive and rarefactive IASWs is studied and, for example, effect of temperature of positive ions and number density of hot electrons on polarity of IASWs is numerically investigated.

Pressure-induced metallization in the absence of a structural transition in the layered transition-metal dichalcogenide ZrSe2.

First-principles calculations were carried out on the ZrSe2 compound, which has been of interest owing to its technologically important physical properties. The structural, electronic and optical properties of this compound were investigated under pressure through the plane wave pseudopotential approach within the framework of density functional theory. A comparison between the computed crystal structure parameters and the corresponding experimental counterparts shows a very good agreement between them. Fitting the pressure-volume data using the third-order Birch-Murnaghan equation of state yielded a bulk modulus B0 = 38.17 GPa and a pressure derivative of bulk modulus B'0 = 8.2 for hexagonal ZrSe2. The relationship between the band structure and pressure is revealed. We calculated the total density of state (TDOS) under different pressures and partial density of state (PDOS) from 0 to 10 GPa. According to our calculations, metallization of hexagonal ZrSe2 is predicted to occur at around 10 GPa and pressure-induced band-gap engineering reveals the transformation of the indirect to direct band gap with increasing pressure. Furthermore, optical properties, such as the complex dielectric function, refractive index and reflectivity spectra of this compound, were studied for incident electromagnetic waves in an energy range up to 45 eV. The contributions to various transition peaks in the optical spectra are analyzed and discussed with the help of the energy-dependent imaginary part of the dielectric function.

Bifurcation analysis of ion-acoustic superperiodic waves in ultra-relativistic dense plasma

Abstract Bifurcation analysis of ion-acoustic solitary, periodic and superperiodic waves in ultra-relativistic quantum degenerate electron-positron-ion plasma is investigated based on Sagdeev’s pseudopotential approach. The phase plane plots for the superperiodic, periodic, and homoclinic trajectories for the dynamical system are developed. Rarefactive and compressive solitary waves are demonstrated to exist. The influence of plasma parameters on the characteristic properties of the periodic and superperiodic waves is studied. Also, the effect of different plasma parameters on the Sagdeev pseudopotential profile is investigated. The results of this study may be used to shed light on the fundamental properties of nonlinear waves in dense objects (e.g., white dwarfs and neutron stars). These results also may be beneficial in describing laboratory plasma (e.g., interaction experiments of intense laser-solid matter), and plasma applications such as microelectronic devices.

Structural, electronic, optical, mechanical and magnetic properties of Co2CrZ (Z = As, B, Ga, Pb) full-Heusler compounds

Two separate computational algorithms have been used in the current investigation of Full-heusler compounds. One is the pseudo-potential approach used in the Atomistic Tool Kit-Virtual Nanolab, while the other is FP-LAPW method as implemented in WIEN2k. In the computational code, these compounds exhibit mattelic character in both the majority and minority spin channels. According to the WIEN2k and ATK-VNL codes, the computed magnetic moments of these compounds Co2CrZ (Z = As, B, Ga, and Pb) are 4.93 µB and 5.02 µB, 3.00 µB and 3.08 µB, 3.02 µB and 3.16 µB, and 4.07 µB and 4.30 µB, respectively. Between the estimated value and the Slater-Pauling rule, we discovered excellent agreement. These compounds' optical characteristics include reflectivity, refractive index, excitation coefficient, and absorption coefficient, among others. An analysis has been done on the electron energy loss and optical conductivity. Both the electron energy-loss function and the absorption coefficient increase as the energy value increases. As per the results of elastic properties, Co2CrZ compounds with Z = As, Pb are ductile by nature, whereas those with Z = B, Ga are brittle. Co2CrZ (Z = As, B, Ga, and Pb) compounds exhibit metallic behaviour when their Cauchy pressure (CP = C12 - C44) value is positive.

Stochastic and mixed density functional theory within the projector augmented wave formalism for simulation of warm dense matter.

Stochastic density functional theory (DFT) and mixed stochastic-deterministic DFT are burgeoning approaches for the calculation of the equationof state and transport properties in materials under extreme conditions. In the intermediate warm dense matter regime, a state between correlated condensed matter and kinetic plasma, electrons can range from being highly localized around nuclei to delocalized over the whole simulation cell. The plane-wave basis pseudopotential approach is thus the typical tool of choice for modeling such systems at the DFT level. Unfortunately, stochastic DFT methods scale as the square of the maximum plane-wave energy in this basis. To reduce the effect of this scaling and improve the overall description of the electrons within the pseudopotential approximation, we present stochastic and mixed DFT approaches developed and implemented within the projector augmented wave formalism. We compare results between the different DFT approaches for both single-point and molecular dynamics trajectories and present calculations of self-diffusion coefficients of solid density carbon from 1 to 50eV.

Theoretical investigation on the structural and vibrational properties of some alkali liquid metals: A pseudopotential approach

Along with a few elastic constants, a recently created pseudopotential is employed to examine the vibrational properties of some simple alkali metals, i.e. Li, Na, K, Rb and Cs. The phonon dispersion curves (PDC) are computed in the text. (ωL and ωT), longitudinal sound velocity (vl), transverse sound velocity (vt), isothermal bulk modulus (B), modulus of rigidity (G), Young’s modulus (Y ), Debye temperature (θD) of some liquid alkali metals. The second order technique used in the current work, using Hubbard and Beeby (HB) equations, is based on pseudopotential theory. The various Percus-Yevick hard sphere (PYHS) and one-component plasma (OCP) structure factors used in the current investigation are used to construct the pair correlation function g(r). The current paper makes use of three distinct forms of local field correction functions developed by Hartree (H), Taylor (T), and Nagy (N). The current findings are found to qualitatively agree with the experimental and theoretical data that is currently available.

Structural, electronic, optical and vibrational properties of CdSiP2 from first-principles

We report the results of a first-principles research of the structural, electronic, linear and nonlinear responses, and vibrational properties of CdSiP2 based on the density functional theory using pseudopotential plane-wave approach. We calculate the energy band structure, dielectric function, absorption coefficient, reflectivity, refractive index, SHG susceptibility, and phonon dispersion curves. In order to obtain accurate band gap value of CdSiP2, the GW approximation method is used to calculate the quasiparticle band structure and the corrected band gap value is in excellent agreement with experimental measurements. Furthermore, the corrected band gap can be used as scissor shift for linear and nonlinear optical properties calculations. The linear-response theory is used to derive the phonon dispersion curves and density of states. All zone-center phonon modes are calculated and LO-TO splitting of the infrared modes are identified. The results show a good agreement with available experimental data and other calculations.

Wave breaking amplitudes of Langmuir modes in electron-positron-ion-dusty plasmas

In contrast to the conventional studies on low frequency dust acoustic or dust ion acoustic waves, the investigation is done here on the wave characteristics of high frequency Langmuir modes in electron-positron-ion-dusty plasmas. In the wave analysis, the electrons, positrons, and ions are considered to follow relativistic dynamics. Whereas negative or positive polarity massive dust grains form a fixed charge neutralizing background. Within the Sagdeev pseudopotential approach, the wave breaking amplitudes of such high frequency oscillations are derived. The wave breaking amplitudes are shown to depend on various system parameters like equilibrium ion-to-electron density ratio, relativistic Lorentz factor associated with the phase velocity of oscillations, etc. It has been demonstrated that, even though the dust grains do not participate in the wave dynamics, the nature of their charge polarity and the values of equilibrium dust density have profound effects on the wave breaking amplitudes. We expect that the results of our investigation in such dusty plasma medium may have some relevance in the space plasma research.

Finite Difference Interpolation for Reduction of Grid-Related Errors in Real-Space Pseudopotential Density Functional Theory.

The real-space pseudopotential approach is a well-known method for large-scale density functional theory (DFT) calculations. One of its main limitations, however, is the introduction of errors associated with the positioning of the underlying real-space grid, a phenomenon usually known as the "egg-box" effect. The effect can be controlled by using a finer grid, but this raises the cost of the calculations or even undermines their feasibility altogether. Therefore, there is ongoing interest in the reduction of the effect per a given real-space grid. Here, we present a finite difference interpolation of electron orbitals as a means of exploiting the high resolution of the pseudopotential to reduce egg-box effects systematically. We implement the method in PARSEC, a finite difference real-space pseudopotential DFT code, and demonstrate error mitigation and improved convergence at a low additional computational cost.

Opto-electronic and thermoelectric properties of XMgY (X=Li, Na; Y=Al, Ga) alloys: GGA and SCAN based approaches

The half Heusler alloys are important class of materials which are utilized for memory as well as the spintronic devices. The thermoelectric response calculations are also reported for Heuslers alloys. In this research work, electronic dispersion curves, thermoelectric and optical parameters of XMgY (X=Li, Na/Y=Al, Ga) half Heuslers have been investigated by employing the pseudopotential approach along side the Boltzmann transport theory. The XMgY (X=Li, Na/Y=Al, Ga) were reported stable in C1b type structure by energy-volume optimization, Born stability criteria on elastic constants and positive phonon modes in full zone in phonon dispersion curves by Afaq et al. Both the SCAN and Generalized Gradient Approximation proved these alloys metallic in nature. To understanding the complex phenomenon of electron flow inside a material, Fermi surfaces are studied and discussed. The different thermoelectric response parameters are computed in temperature range 300 to 1200 K. The comprehensive analysis of imaginary part of dielectric constant predicts the utility of these alloys in sensors and opto-electronic devices.

Simulated sulfur K-edge X-ray absorption spectroscopy database of lithium thiophosphate solid electrolytes

X-ray absorption spectroscopy (XAS) is a premier technique for materials characterization, providing key information about the local chemical environment of the absorber atom. In this work, we develop a database of sulfur K-edge XAS spectra of crystalline and amorphous lithium thiophosphate materials based on the atomic structures reported in Chem. Mater., 34, 6702 (2022). The XAS database is based on simulations using the excited electron and core-hole pseudopotential approach implemented in the Vienna Ab initio Simulation Package. Our database contains 2681 S K-edge XAS spectra for 66 crystalline and glassy structure models, making it the largest collection of first-principles computational XAS spectra for glass/ceramic lithium thiophosphates to date. This database can be used to correlate S spectral features with distinct S species based on their local coordination and short-range ordering in sulfide-based solid electrolytes. The data is openly distributed via the Materials Cloud, allowing researchers to access it for free and use it for further analysis, such as spectral fingerprinting, matching with experiments, and developing machine learning models.

Structural, elastic, and thermodynamic properties of BaXCl3 (X = Li, Na) perovskites under pressure effect: ab initio exploration

In this study, we employed the ab initio pseudopotential plane wave approach, utilizing the GGA-PBEsol exchange-correlation functional, to investigate the structural, elastic, and thermodynamic properties of BaXCl3 (X = Li, Na) perovskites under hydrostatic pressures ranging from 0 to 18 GPa. Apart from utilizing the GGA-PBEsol functional, this study also employed the GGA-PBE, GGA-WC, and LDA functionals to simulate the exchange-correlation interactions for computing the structural parameters. Our results show that the optimized lattice parameters are in good agreement with previously predicted values. Based on the calculated elastic moduli of a single crystal, we found that both BaLiCl3 and BaNaCl3 perovskites retain mechanical stability under hydrostatic pressures of up to 18 GPa. Furthermore, we calculated several other important parameters that describe the polycrystalline aggregates of these compounds, including the modulus of compressibility, the shear modulus, the Poisson’s ratio, Young’s modulus, the speeds of sound, and the Debye temperature. Additionally, we examined the temperature and pressure dependencies of the thermal coefficients of the perovskites using the quasi-harmonic approximation. Notably, all of the results presented in this study are reported for the first time and require further confirmation through experimental investigations. We hope that our findings contribute to a more comprehensive understanding of the structural and thermodynamic properties of BaXCl3 (X = Li, Na) perovskites under pressure.

Study of single-component two-phase free energy lattice Boltzmann models using various equations of state

In single-component two-phase flow simulations by the lattice Boltzmann method (LBM), one key topic of interest is the equation of state (EOS), which has been studied more in the pseudo-potential approach but much less in the free energy approach. Here, we conducted fair assessment of several popular non-ideal gas EOS in free energy LBM. The inability to independently tune the surface tension and interface thickness was identified for existing free energy formulation using most EOS. A simple modification was proposed and incorporated into three free energy LBM models, including the pressure tensor model, Lee–Fischer's model, and Guo's well-balanced model. Good compatibility with all of them was demonstrated by numerical simulations. In addition, a piecewise-linear (PWL) EOS proposed in pseudo-potential LBM was found to be also feasible in free energy LBM. Extensive numerical experiments on diverse problems (some containing contact lines) revealed that the influence of EOS was rather limited when key parameters are nearly the same (easily achievable with the proposed modification). The capability of the Lee–Fischer and well-balanced models to reduce the spurious currents down to machine accuracy (for static drop tests) was found to be independent of the EOS (including the customized PWL EOS). Overall, the pressure tensor LBM is associated with larger spurious currents and deviations in the density and chemical potential, thus less accurate than the other two. However, it is less sensitive to the relaxation parameter and grid number, thus more robust.

A comparative study of Cu-Au, Ag-Au and Ag-Cu alloys: A pseudopotential approach

Using the pseudopotential approach, we have calculated the mechanical characteristics of the alloys Cu-Au, Ag-Au, and Ag-Cu. We have employed pseudopotentials due to Pandya et al. (Physica B, 2001;307:138–149) and Bhatia et al. (Philos. Mag., 2021;101(13): 1602–1618) to calculate PDC (Phonon dispersion curves), P-DoS (Phonon density of states), WT (Debye-Waller factor), u¯2 (mean square displacement), heat capacity (CP), elastic constants (C11, C12 and C44), bulk modulus (B) and anisotropic factor (A). In the absence of experimental research, theoretical findings of PDC for alloys AgAu3 and AgCu3 (excluding CuAu3) are provided for the first time, which may be used to estimate the comprehensive physical characteristics. Our elastic constants findings agree with existing experimental results. These pseudopotentials have been found successfully for the study of solid as well as liquid metal properties.

On One Widely-Spread Inaccuracy and Its Elimination in the Theories of Nonlinear Electrostatic Waves in Plasma Based on the Sagdeev’s Pseudopotential Approach

On One Widely-Spread Inaccuracy and Its Elimination in the Theories of Nonlinear Electrostatic Waves in Plasma Based on the Sagdeev’s Pseudopotential Approach

Oblique propagation of arbitrary amplitude ion acoustic solitary waves in anisotropic electron positron ion plasma

The oblique propagation of arbitrary ion acoustic solitary waves (IASWs) in magnetized electron-positron-ion plasmas is investigated by employing Sagdeev pseudopotential approach. Ions are assumed to be adiabatic having anisotropic thermal pressure. Electrons and positrons are considered to be isothermal, following Maxwellian distribution. In terms of electrostatic potential, Sagdeev potential function is obtained and analyzed numerically in the context of relevant plasma configuration parameters. The existence region of solitary pulses is defined accurately. It is investigated how several plasma configuration parameters, such as the positron concentration, parallel, and perpendicular ion pressure affect soliton characteristics.

Phase stability and physical properties of lanthanum dicarbide under pressure

ABSTRACT First-principles calculations of electronic parameters, mechanical and dynamical stabilities on superconducting properties of the body-centered tetragonal intermetallic lanthanum dicarbide LaC2 have been reported at zero and high pressures. The investigated properties have been established through both full-potential-linearized augmented plane wave (FP-LAPW) and plane-wave pseudopotential (PW-PP) approaches, in conjunction with the generalized gradient approximation (GGA). Our investigations validate that the LaC2 crystal has a mechanical and dynamical stability under normal conditions. The generalised mechanical stability criteria applied to compressed LaC2, suggest that the compound remains stable for pressures below 18.30 GPa. The evaluated superconducting critical temperature Tc and the electron–phonon coupling parameter λ at zero pressure are found to be in excellent concordance with the experimental data. Furthermore, at elevated pressures, Tc and λ are predicted to decrease and the normalised specific heat jump remains unchanged.