Pseudopotential Approach Research Articles

Ab-initio calculations of shallow dopant qubits in silicon from pseudopotential and all-electron mixed approach

Obtaining an accurate first-principle description of the electronic properties of dopant qubits is critical for engineering and optimizing high-performance quantum computing. However, density functional theory (DFT) has had limited success in providing a full quantitative description of these dopants due to their large wavefunction extent. Here, we build on recent advances in DFT to evaluate phosphorus dopants in silicon on a lattice comprised of 4096 atoms with hybrid functionals on a pseudopotential and all-electron mixed approach. Remarkable agreement is achieved with experimental measurements including: the electron-nuclear hyperfine coupling (115.5 MHz) and its electric field response (−2.65 × 10−3 μm2/V2), the binding energy (46.07 meV), excited valley-orbital energies of 1sT2 (37.22 meV) and 1sE (35.87 meV) states, and super-hyperfine couplings of the proximal shells of the silicon lattice. This quantitative description of spin and orbital properties of phosphorus dopant simultaneously from a single theoretical framework will help as a predictive tool for the design of qubits.

Structural properties of NaBeH3 material: Ab-initio calculations

Ab-initio calculations from first principle methods were performed toinvestigate the structural properties of perovskite-type hydride NaBeH3material. The pseudopotential plane-wave approach in the framework ofdensity functional theory (DFT) as implemented in the ABINIT codecomputer was used. The exchange-correlation functional for all elementsof our material of interest was described with the local densityapproximation (LDA). Our results of the equilibrium lattice parameter, thebulk modulus, and the pressure derivative of the bulk modulus of cubicNaBeH3 semiconducting material were found at around 3.335 Å (3.339Å), 65.64 GPa and 3.56, respectively. Our data are in good agreementwith the available theoretical data of the literature. In addition, the meltingpoint of our material of interest was calculated and found equal to 1217.45K. To the best of the authors' knowledge, no data is available in theliterature on the melting point of NaBeH 3 material.
 

Investigation of electronic structure, electrical and thermal properties of PbS quantum dots for thermoelectric applications

PbS nanoparticles (NPs) and PbS quantum dots (QDs) were prepared by co-precipitation method and simple chemical bath method, respectively and their thermoelectric properties were comparatively investigated. The structural, morphological, optical, functional groups and pore size of PbS NPs and PbS QDs were analysed by XRD, UV-DRS, FTIR and BET analysis. TEM images revealed spherical morphology of PbS QDs with size ranging from 5 to 10 nm. The band gap value of PbS QDs calculated from UV-DRS is 1.20 eV which is relatively higher compared to PbS NPs (0.73 eV). This may due to the effect of quantum confinement. From the BET analysis the specific surface area was obtained as 66.031 m2 g−1. Quantum Espresso package based on Plane Wave-based Pseudopotential (PWSCF) approach was used to calculate the energy spectrum of PbS QDs of various sizes. The calculated energy gap value between the HOMO and LUMO levels is found to vary with PbS cluster size. Thermoelectric measurements showed that pelletized sample of PbS QDs exhibit a large Seebeck coefficient, high power factor and low thermal conductivity resulted in large figure of merit. The figure of merit of pelletized sample of PbS QDs at 403 K is 0.34 which is relatively higher than that of pelletized PbS NPs (0.24) at the same temperature, making it highly suitable for thermoelectric applications.

DFT Study of ScP and AlP in B1, B2, and B3 Phases at Ambient Pressure

Structural, electronic, elastic, and dynamic characteristics of scandium phosphide and aluminium phosphide compounds are studied theoretically. The study has been performed for rock salt (B1), CsCl (B2), and zinc blend (B3). We use the density functional theory, which is based on the plane wave basis and the pseudopotential approach, as implemented in the Quantum Espresso Software package. ScP and AlP exhibits metallic behavior in the B1 and B2 phases. The B3 phase of ScP displays a semiconductor characteristic with a broad and straight band gap at X of (1.617). In AlP, the B3 phase exhibits semiconductor characteristics with an indirect band gap at Г-X of (1.60). Both compounds ScP and AlP on B1, B2, and B3 structures report computed ground state parameters. The zinc blend phase is the most stable of the three phases, according to the findings. Our computed results are in good agreement with earlier investigations. The work presented in this article is related to sustainable development goals (SDGs) to transform our world regarding industry, innovation, and infrastructure.

Exciton properties, optical phonon modes, polaron characteristics and plasma frequency of GaSb upon compression

The pressure dependence of exciton properties, optical phonon modes, polaron characteristics and plasma frequency of GaSb has been investigated using a pseudopotential approach combined with Harrison and Adachi's models. The obtained results show reasonable accord with data available in the literature. The enhanced pressure from 0 to 40 kbar increases the exciton reduced mass monotonously and in a non-linear way. The screening effect makes the Bohr radius much larger than the lattice parameter of these semiconductor materials. The phonon frequency modes increase with increasing pressure. This is due to the pressure effect that brought atoms closer to each other and thus they sit in steeper potential wells. The Fröhlich coupling constant decreases monotonously with increasing pressure. This reflects the reduction of the lattice asymmetrical local deformation when GaSb is subjected to pressure. The applied pressure makes the plasma system of GaSb creates longer wavelengths which give ions a large amount of kinetic energy. The information obtained from this contribution may become good guidance for use of the material in question in several device applications, e.g., in infrared optical sources and thermo photovoltaic systems.

Modified AKNS model, Riccati-type pseudo-potential approach and infinite towers of quasi-conservation laws

In this paper, a dual Riccati-type pseudo-potential formulation is introduced for a modified AKNS system (MAKNS) and infinite towers of novel anomalous conservation laws are uncovered. In addition, infinite towers of exact nonlocal conservation laws are uncovered in a linear formulation of the system. It is shown that certain modifications of the nonlinear Schrödinger model (MNLS) can be obtained through a reduction process starting from the MAKNS model. So, the novel infinite sets of quasi-conservation laws and related anomalous charges are constructed by an unified and rigorous approach based on the Riccati-type pseudo-potential method, for the standard NLS and modified MNLS cases, respectively. The nonlocal properties, the complete list of towers of infinite number of anomalous charges and the (nonlocal) exact conservation laws of the quasi-integrable systems, such as the deformed Bullough–Dodd, Toda, KdV and SUSY sine-Gordon systems, can be studied in the framework presented in this paper. Our results may find many applications since the AKNS-type system arises in several branches of nonlinear physics such as Bose–Einstein condensation, superconductivity and soliton turbulence.

Performance of the modified Becke–Johnson potential employing the pseudopotential plane-wave approach for band structure calculations

The modified Becke–Johnson exchange potential combined with local-density approximation correlation (mBJLDA) has recently attracted interest because it provides highly improved band gaps at a very low computational cost. In this work we performed an extensive investigation of the performance of the mBJLDA potential employing a norm-conserving pseudopotential plane-waves approach (mBJLDA@PP), as implemented in the abinit code, using a test set of 83 solids representing a wide range of semiconductors and insulators. Our results confirm the conclusion of our previous study that the number of electrons treated as valence in the pseudopotentials of the cations can have a significant impact on the calculated mBJLDA@PP band gaps. More specifically, while the use of typical pseudopotentials leads to accurate band gaps of certain systems, it yields significantly underestimated band gaps for other systems compared to experiment and to those of the all-electron mBJLDA (mBJLDA@AE) approach. The classes of the latter systems are identified, and this problem is resolved by including some outer core states as valence. The resulting mean absolute error in the calculated band gaps (compared to experiment) is of 0.46 eV, which is comparable to that of the mBJLDA@AE band gaps, reflecting the accuracy and reliability of the mBJLDA@PP approach for the band gap calculations.

Physical aspects of cnoidal waves in non-thermal electron-beam plasma systems

The effects of electron beam and non-thermal electrons on ion-acoustic cnoidal waves (IACWs) structure in a two-fluid plasma system are investigated. A Kappa-Cairns type distribution is assumed for the background electrons. The Korteweg–de Vries (K-dV) equation is obtained by employing reductive perturbation technique and the analytical solution of K-dV equation is derived by employing the Sagdeev pseudo-potential approach. It is seen that in the presence of the electron beam, four modes can exist in this plasma model. In this study, it is observed that only two modes are real in all cases. Furthermore, it is found that the characteristics of the ion-acoustic cnoidal wave depend strongly on the electron beam parameters (via and ) as well as the non-thermal indexes for the plasma electrons (via and ).

Dust ion acoustic solitons and double layers in a dusty plasma with adiabatic positive dust, adiabatic positive ion species, and Cairns-distributed electrons

The propagation of dust ion acoustic solitary waves and double layers is studied in a dusty plasma with heavy adiabatic positively charged dust grains and lighter adiabatic positive ions with Cairns-distributed electrons using the arbitrary amplitude Sagdeev pseudopotential approach. The analysis of the Sagdeev pseudopotential shows that this plasma model supports the propagation of positive solitons limited by the occurrence of the ion sonic point and negative solitons limited by the occurrence of double layers. Solitons of both polarities coexist for a range of some plasma parameters. We have shown that at a critical dust-to-ion density ratio, f, at which the third derivative of the Sagdeev pseudopotential vanishes, positive and negative solitons coexist without a soliton with finite amplitude at the acoustic speed, contrary to an earlier study. This suggests that the existence of a soliton with finite amplitude at the acoustic speed is not always a pre-requisite for the coexistence of nonlinear structures of both polarities. Positive and negative solitons coexist when the electrons are strongly nonthermal, with moderate ion thermal effects. Increasing ion thermal effect shifts the coexistence region to lower values of f, and when the ion thermal effects become important, negative solitons disappear and only positive solitons survive. The effects of different plasma parameters on the characteristics of the nonlinear structures have also been discussed in detail.

Engineering the hydrogen storage properties of the perovskite hydride ZrNiH3 by uniaxial/biaxial strain

In the present work, the bonding length, electronic structure, stability, and dehydrogenation properties of the Perovskite-type ZrNiH3 hydride, under different uniaxial/biaxial strains are investigated through ab-initio calculations based on the plane-wave pseudo-potential (PW-PP) approach. The findings reveal that the uniaxial/biaxial compressive and tensile strains are responsible for the structural deformation of the ZrNiH3 crystal structure, and its lattice deformation becomes more significant with decreasing or increasing the strain magnitude. Due to the strain energy contribution, the uniaxial/biaxial strain not only lowers the stability of ZrNiH3 but also decreases considerably the dehydrogenation enthalpy and decomposition temperature. Precisely, the formation enthalpy and decomposition temperature are reduced from −67.73 kJ/mol.H2 and 521 K for non-strained ZrNiH3 up to −33.73 kJ/mol.H2 and 259.5 K under maximal biaxial compression strain of ε = −6%, and to −50.99 kJ/mol.H2 and 392.23 K for the maximal biaxial tensile strain of ε = +6%. The same phenomenon has been also observed for the uniaxial strain, where the formation enthalpy and decomposition temperature are both decreased to −39.36 kJ/mol.H2 and 302.78 K for a maximal uniaxial compressive strain of ε = - 12%, and to −51.86 kJ/mol.H2 and 399 K under the maximal uniaxial tensile strain of ε = +12%. Moreover, the densities of states analysis suggests that the strain-induced variation in the dehydrogenation and structural properties of ZrNiH3 are strongly related to the Fermi level value of total densities of states. These ab-initio calculations demonstrate insightful novel approach into the development of Zr-based intermetallic hydrides for hydrogen storage practical applications.

Ground-state energy of quasi-free positrons in non-polar fluids

We have calculated the background energy (V0) for positrons in noble gases with an ab initio potential and the Wigner-Seitz (WS) ansatz. In contrast to the general pseudo-potential approach, we have used accurate ab initio potentials for the positron-atom interaction. The ansatz includes an assumed form of the potential, resulting from an average over fluid atoms, and we propose four different options for this. By comparing the different options to literature data for an effective electron number (Zeff), we find that agreement can be obtained for light elements but fails for heavy elements. We suspect that the strong polarizability of the heavy elements makes the simple potential averaging, as assumed in the WS model, insufficient to fit the measurements without also making use of pseudo-potentials. We also raise our suspicion that the comparison of annihilation rates between ground-state calculations and experimental values is not appropriate. Furthermore, the congruence of V0 to Zeff values predicted by a contact potential approximation appears to be invalidated by our results.

Ion core effect on scattering processes in dense plasmas

A pseudopotential approach was used to study the effect of an ionic core on the electron–ion scattering in dense plasmas. Screening of the ion charge is taken into account using the density response function in the long wavelength limit. Additionally, the effect of electronic non-ideality is included using the compressibilty sum-rule connecting the local field correction and the exchange-correlation part of the electronic free energy density. Using a screened pseudopotential, we have computed electron–ion scattering phase shifts, the total elastic scattering cross section, and the transport cross section. It is found that the ionic core leads to the strong decrease in the scattering cross sections. Additionally, it is shown that the transport cross section has a non-monotonic dependence on the variation of the ionic core field parameters.

Elastic and inelastic particles scattering by dust acoustic soliton. A new oscillatory process in dusty plasma

The parameters of scattering (reflection) of charged particles by the leading edge of a dust acoustic soliton are analyzed. The soliton profile is calculated using the Sagdeev pseudopotential approach. To analyze the motion of charged particles, the Newton’s second law is used. It is shown theoretically that the charged particle scattering can be elastic and inelastic. The nature of scattering significantly depends on the presence of dissipation. In the dissipative case, charged particles scattering is the process of an oscillatory nature. It is shown that it can be considered as a new type of oscillations of charged particles in plasma. The parameters of the oscillations are calculated both numerically (nonlinear case) and analytically (within the linear approximation). Theoretical results are compared with known experimental results, as well as the applied aspect is stated.

Screening in Graphene: Response to External Static Electric Field and an Image-Potential Problem.

We present a detailed first-principles investigation of the response of a free-standing graphene sheet to an external perpendicular static electric field E. The charge density distribution in the vicinity of the graphene monolayer that is caused by E was determined using the pseudopotential density-functional theory approach. Different geometries were considered. The centroid of this extra density induced by an external electric field was determined as = 1.048 Å at vanishing E, and its dependence on E has been obtained. The thus determined was employed to construct the hybrid one-electron potential which generates a new set of energies for the image-potential states.

Solitary waves and double layers in complex plasma media

A complex plasma medium (containing Cairns nonthermal electron, adiabatically warm inertial ion, and stationary positively charged dust (PCD) species (making a plasma system very complex) is considered. The effects of PCD species, nonthermal electron species, and adiabatic ion-temperature on ion-acoustic (IA) solitary waves (SWs) and double layers (DLs) are investigated by the pseudo-potential approach, which is valid for the arbitrary amplitude time-independent SWs and DLs. It is observed that the presence of the PCD species reduces the phase speed of the IA waves, and consequently supports the IA subsonic compressive SWs in electron-ion-PCD plasmas. On the other hand, the increase in both adiabatic ion-temperature and the number of nonthermal or fast electrons causes to reduce the possibility for the formation of subsonic SWs, and thus convert subsonic SWs into supersonic ones. It is observed that after at a certain value of the nonthermal parameter, the IA supersonic SWs with both positive and negative potentials as well as DLs with only negative potential exist. The applications of the work in space environments (viz. Earth's mesosphere, cometary tails, Jupiter's magnetosphere, etc.) and laboratory devices, where warm ion and nonthermal electron species along with PCD species have been observed, are briefly discussed.

A fully nonlinear solitary wave in six-component dusty cometary plasma

The dynamics of fully nonlinear structure of six-component dusty cometary plasma system with the help of Sagdeev pseudo-potential techniques have been investigated. This plasma system is made up of Oxygen (positively and negatively charged) ion pair, negatively charged dust particles, and kappa distributed ions of Hydrogen, hot solar electrons and slightly colder cometary electrons. The linear analysis is carried out and the linear dispersion relation is obtained and investigated with some relevant plasma parameters. As a result, the velocities in the fluid equations are normalized to a general acoustic speed instead of the particular form of acoustic speed. Employing pseudo-potential approach, the basic equations of plasma system were reduced to a single nonlinear ordinary differential equation (energy-balance). By means of Sagdeev potential curves and bifurcation analysis of phase-portrait, the existence and propagation of nonlinear waves are examined. In addition to the periodic solution, it is shown that the localized negative and positive amplitude electrostatic pulses may (co-) exist and propagate in plasma system depending on the Mach number intervals. The impact of some intrinsic plasma parameters on the main features of the solitary wave electrostatic potential profile and the associated electrostatic field are extensively investigated. The results of this research are relevant to plasmas in both laboratory plasmas and exclusively in space plasmas as, comet tails, rings of giant planets, solar wind, interstellar clouds, etc.

Investigation of phase evolution and Gd occupation in (Lu1-xGdx)2SiO5 lattice by Rietveld refinement and DFT simulation

Cerium-doped lutetium oxyorthosilicate (LSO:Ce, Lu2SiO5:Ce) is considered to be a typical scintillator with comprehensive good scintillation properties. The doping of Gd3+ elements with different concentrations strongly influences the structure and luminescence performance of LSO. The full concentration range of LGSO ((Lu1-xGdx)2SiO5) powders were prepared using a sol-gel method. The influences of the doping Gd3+ ion concentration on the phase evolution and lattice parameters of LGSO were investigated via X-ray diffraction (XRD), Rietveld refinement and density functional theory (DFT) simulations. It was found that the monoclinic crystal structure of LGSO gradually transitioned from C2/c to P21/c under elevated temperatures and phase transition temperature varied from 975 to 1400 ​°C as Gd replaced Lu. The lattice constants (a, b, and c) of LGSO lattice increased with the addition of Gd. The Rietveld refinement results indicate that doping Gd3+ in LGSO was prone to occupy the RE1 site rather than the RE2 site and Gd dopants was easily to form GdRE1-GdRE1 defect complex. The formation energy results of Gd3+ replacing different Lu3+ sites calculated by using the first-principles pseudopotential approach further proved this occupation mode. The intensity of photoluminescence of Ce:(Lu1-xGdx)2SiO5 attained the peak value when the content of Gd doping reached 0.05.

Ab initio study of the structure, elastic, and electronic properties of Ti3(Al1\u2212nSin)C2 layered ternary compounds

The MAX phase materials such as layered ternary carbides that simultaneously exhibit characteristics of metallic and ceramic materials have received substantial interest in recent years. Here, we present a systematic investigation of the electronic, structural stabilities, and elastic properties of Ti3(Al1−nSin)C2 (n = 0,1) MAX phase materials using the ab initio method via a plane-wave pseudopotential approach within generalized-gradient-approximations. The computed electronic band structures and projected density of states show that both Ti3SiC2 and Ti3AlC2 are metallic materials with a high density of states at the Fermi level emanating mainly from Ti-3d. Using the calculated elastic constants, the mechanical stability of the compounds was confirmed following the Born stability criteria for hexagonal structures. The Cauchy pressure and the Pugh’s ratio values establish the brittle nature of the Ti3SiC2 and Ti3AlC2 MAX phase materials. Due to their intriguing physical properties, these materials are expected to be suitable for applications such as thermal shock refractories and electrical contact coatings.

Solitary waves in a cometary plasma with heavy dust ion pairs

Multicomponent plasma in an astrophysical environment comprising wind electrons, cometary electrons, positive and negative dust ions, and lighter hydrogen ions was studied earlier by a pseudo-potential approach. The coma of comet Halley is reported to comprise many heavier positive and negative ions. Thus, we generalize the soliton solution for a plasma consisting of multiple pair-ion dust species. Heavier atomic and molecular ions are considered as dust ions in this model. The lighter ions and electrons are modeled by Kappa distribution. We find that the presence of multiple dust pair ions enhances soliton amplitude. The effect of the temperature and density of lighter ions gives insight into the switching of compressive and rarefractive nature of the solutions. The compressive and rarefractive regimes of these solitary waves are analyzed and reported for the first time.

Effect of spin-orbital coupling on the electronic, mechanical, thermoelectric, and vibrational properties of XPtBi (X = Sc and Y): A first-principles study

Heusler compounds constitute a versatile class of materials, as evidenced by their numerous technological applications. Herein, we report a comparative study of the electronic, mechanical, vibrational, and thermoelectric properties of half-Heusler compounds XPtBi (X = Sc and Y) based on first-principles calculations, with and without spin-orbital coupling (SOC). The plane-wave pseudo-potential approach within density functional theory (DFT) and the Boltzmann transport equations have been used to compute these properties. SOC has a considerable effect on the electronic band structures of XPtBi (X = Sc and Y), leading to band inversion without breaking any symmetry. This band inversion results in the emergence of a topological phase in ScPtBi and YPtBi. Phonon dispersion curves and phonon densities of state have been calculated for these compounds, with and without SOC, for comparison. The calculations also reveal that, with the inclusion of SOC, these materials have improved thermoelectric properties, with figures of merit (ZT) of 0.41 for ScPtBi and 0.35 for YPtBi at 1200 K. Hence, these are promising thermoelectric materials for use at higher temperatures.