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Lithium-ion batteries employing graphite as the anode material are now widely used in powering electronic gadgets like, mobile phones, laptops, electronic watches and calculators and also to provide required power to run engine of electric vehicles. However, storage capacity, open circuit voltage, energy density and battery life are the major considerations on which researchers are trying different alternatives to achieve better performance of the battery. In this research, Beryllium-doped and defective graphenes have been investigated by employing the ab initio DFT method. It has been found that graphene with a defect and Be–doped graphene with defects can serve as an efficient materials for anode in Li-ion batteries. [ABSTRACT FROM AUTHOR]

Applying the principle of Density functional theory, we can calculate various parameters like lattice constant, band gap, band plot, dielectric function plot, refractive index plot, conductivity plot, density of state plot, loss function etc. of GaN. In this work, we use different electronic pseudopotentials with different relativistic treatment studied using Local density approximation functional (LDA-CAPZ) within DFT for GaN. We used to calculate the energy values, lattice parameters change after geometry optimisation and plot the band energies. Electronic structure calculations results are compares taking different electronic pseudopotentials of different cut-off energy having different relativistic approaches. The Density of state plot and partial density of states plot help to studied more about the electronic as well as magnetic characteristics of the GaN sample. Here, we also compare the advantages and disadvantages of different pseudopotentials with different relativistic approaches of the sample. Energy level distribution and partial density of states were compared for all the pseudopotentials with different relativistic treatments, providing insight into the orbital contributions of electrons to the density of levels. Our study provides a deeper understanding into the impact of electronic pseudopotentials and relativistic treatments on the electronic and structural properties of GaN.

A procedure for defining virtual spaces, and the periodic one-electron and two-electron integrals, for plane-wave second quantized Hamiltonians has been developed, and it was validated using full configuration interaction (FCI) calculations, as well as executions of variational quantum eigensolver (VQE) circuits on Quantinuum's ion trap quantum computers accessed through Microsoft's Azure Quantum service. This work is an extension to periodic systems of a new class of algorithms in which the virtual spaces were generated by optimizing orbitals from small pairwise CI Hamiltonians, which we term as correlation optimized virtual orbitals with the abbreviation COVOs. In this extension, the integration of the first Brillouin zone is automatically incorporated into the two-electron integrals. With these procedures, we have been able to derive virtual spaces, containing only a few orbitals, that were able to capture a significant amount of correlation. The focus in this manuscript is on comparing the simulations of small molecules calculated with plane-wave basis sets with large periodic unit cells at the Γ -point, including images, to results for plane-wave basis sets with aperiodic unit cells. The results for this approach were promising, as we were able to obtain good agreement between periodic and aperiodic results for an LiH molecule. Calculations performed on the Quantinuum H1-1 quantum computer produced surprisingly good energies, in which the error mitigation played a small role in the quantum hardware calculations and the (noisy) quantum simulator results. Using a modest number of circuit runs (500 shots), we reproduced the FCI values for the 1 COVO Hamiltonian with an error of 11 milliHartree, which is expected to improve with a larger number of circuit runs. [ABSTRACT FROM AUTHOR]

Abstract An efficient and accurate approach for calculating exact exchange and other two-electron integrals has been developed for periodic electronic structure methods. Traditional approaches used for integrating over the Brillouin zone in band structure calculations, e.g. trapezoidal or Monkhorst-Pack, are not accurate enough for two-electron integrals. This is because their integrands contain multiple singularities over the double integration of the Brillouin zone, which with simple integration methods lead to very inaccurate results. A common approach to this problem has been to replace the Coulomb interaction with a screened Coulomb interaction that removes singularities from the integrands in the two-electron integrals, albeit at the inelegance of having to introduce a screening factor which must precomputed or guessed. Instead of introducing screened Coulomb interactions in an ad hoc way, the method developed in this work derives an effective screened potential using a Filon-like integration approach that is based only on the lattice parameters. This approach overcomes the limitations of traditionally defined screened Coulomb interactions for calculating two-electron integrals, and makes chemistry many-body calculations tractable in periodic boundary conditions. This method has been applied to several systems for which conventional DFT methods do not work well, including the reaction pathways for the addition of H2 to phenol and Au 20 − $_{20}^{-}$ nanoparticle, and the electron transfer of a charge trapped state in the Fe(II) containing mica, annite.

[Display omitted] We analyze data of the pseudopotential files and successive plane-wave calculations, determining the Slater-Condon parameters related to the 4f and 5d shells of the lanthanide atoms. The selected pseudopotentials belong to the PAW (projected augmented wave) technique. The outlined procedures are generally applicable to other cases and classes of pseudopotentials. The extracted Slater-Condon parameters are reproducing the atomic spectral terms emerging from configurations with incomplete occupation of the shells of the atoms considered. The purpose of this study is to use the obtained Slater-Condon parameters for the study of lanthanide luminescence due to f n → f n-1d orbital promotions. The intra-shell F k ff (k = 0,2,4,6) and inter-shell F k fd (k = 0,2,4) or G k fd (k = 1,3,5) Slater-Condon parameters are discussed in free neutral lanthanide atoms, free Ln3+ ions and ionic bodies in LnF 3 lattices. Furthermore, the d-type intra-shell parameters, F k dd (k = 0,2,4), are considered in the same conditions. The methodology applied here consists in the decomposition into Slater-Type Orbital (STO) primitives, followed by the analytic evaluation of the Slater-Condon integrals. The ff intra-shell parameters are affected to a little extent by the condition of the whole atomic body, while the fd inter-shell parameters, as well as the intra-shell dd ones, are undergoing a significant increase in Ln0 → Ln3+ ionization. These parameters undergo a strong reduction (below the neutral atom values) for the ions in LnF 3 lattices, probing then the so-called nephelauxetic effect. The actual calculations yield parameters slightly overestimated, in comparison with the available experimental data. However, they can be used in semiquantitative simulations of spectral features, with potential applications in modeling lanthanide-based phosphors. [ABSTRACT FROM AUTHOR]

We consider radio-frequency ion guides formed by electrodes, which are periodic sequences of circular apertures. With the help of pulse voltages arranged as trains of a special type, a relay-switched sequence of axial distributions of the pseudopotential can be organized along the axis of the system in the form of space waves with alternating maxima and minima, which convey charged particles along the conveying channel. The disadvantage of the proposed conveying technology is the obligatory presence of neutral gas in moderate amounts, which dampens the excess kinetic energy acquired by charged particles in the jump-like switching of the radio-frequency electric field. An advantage of the proposed conveying technology is the simplified form of radio-frequency voltages applied to the electrodes of the device and the flexible control of the guiding velocity in Gas Chromatography–Mass Spectrometry interfaces, for example. [ABSTRACT FROM AUTHOR]

A key reaction underlying the charge transport in iron containing oxides, clays, micas is the Fe 2 + - Fe 3 + exchange reaction between edge-sharing iron octahedra. These reactions facilitate conduction in these minerals by the thermally-activated hopping of small polarons across the lattice. Depending on the mineral and local charge state the small polaron can either encase an electron or hole. The probability for conduction of small polarons depends strongly on the height and adiabicity of the reaction barrier, with larger and more diabatic barriers yielding slow conduction associated with either weak coupling or a large prerequisite rearrangement of the lattice during charge transport. To model these reactions, a first principle electron transfer (ET) method was developed to model the small polaron hopping between the edge-sharing octahedra sites in hematite ( e - polaron), goethite ( e - polaron), and annite ( h + polaron) bulk structures. The ET method is based on electronic structure methods (i.e., plane-wave Density Functional Theory) capable of performing calculations with periodic cells and large size systems efficiently while at the same time being accurate enough to be used in the estimation of the electron-transfer coupling matrix element, V AB , and the electron transfer transmission factor, κ el . The calculations confirmed the existence of small polarons in all three minerals, and the reactions were predicted to be strongly adiabatic. It was found that transfer of a hole in the octahedral layer of annite had an adiabatic barrier of 0.311 eV, and the transfer of an extra electron in hematite and goethite had adiabatic barriers of 0.242 eV and 0.232 eV respectively. The electronic coupling parameters, V AB , were found to be 0.188 eV, 0.196 eV, and 0.102 eV respectively for hematite, goethite, and annite. While similar bonding topologies pertain, the findings reveal the importance of subtle differences in local structure. [ABSTRACT FROM AUTHOR]

Following on from a previous work (Punter et al., IJQC 2019, 119, 23), pseudopotential sets are developed and tested for a variety of sp2 and sp3 carbon fragments. These fragments contain only one or two explicit protons and electrons, and make use of non‐atom‐centered potentials. They are tested with density functional theory calculations in a selection of chemical environments in which several physical characteristics, including orbital and first ionization energies, are found to be well reproduced. They are then employed in the reproduction of molecular absorption spectra for large organic molecules and carbon allotropes, and are found to recreate both absorption and electronic circular dichroism spectra to a high accuracy. They are also found significantly to increase the computational efficiency of time dependent density functional theory (TDDFT) calculations in which they are used. [ABSTRACT FROM AUTHOR]

An efficient and accurate approach for calculating exact exchange and other two-electron integrals has been developed for periodic electronic structure methods. Traditional approaches used for integrating over the Brillouin zone in band structure calculations, e.g. trapezoidal or Monkhorst-Pack, are not accurate enough for two-electron integrals. This is because their integrands contain multiple singularities over the double integration of the Brillouin zone, which with simple integration methods lead to very inaccurate results. A common approach to this problem has been to replace the Coulomb interaction with a screened Coulomb interaction that removes singularities from the integrands in the two-electron integrals, albeit at the inelegance of having to introduce a screening factor which must precomputed or guessed. Instead of introducing screened Coulomb interactions in an ad hoc way, the method developed in this work derives an effective screened potential using a Filon-like integration approach that is based only on the lattice parameters. This approach overcomes the limitations of traditionally defined screened Coulomb interactions for calculating two-electron integrals, and makes chemistry many-body calculations tractable in periodic boundary conditions. This method has been applied to several systems for which conventional DFT methods do not work well, including the reaction pathways for the addition of H2 to phenol and Au 20 − nanoparticle, and the electron transfer of a charge trapped state in the Fe(II) containing mica, annite. [ABSTRACT FROM AUTHOR]

The present contribution reports on the electronic and optical properties of zinc-blende CdTe quantum dots using a pseudopotential approach. Our findings showed that the predicted nano-structured direct band gap is significantly increased relative to the bulk one. For a nanocrystal diameter in the range 1.2-5 nm, the refractive index and dielectric constant are found to be highly reduced relative the bulk values. Beyond a nanocrystal diameter of 5 nm, the size dependence of all features of interest becomes weak and tends towards retrieving the bulk value.

Modern molecular spectroscopy of diatomic molecules is the precision study of the structure and dynamics of electronically excited states of isolated molecules in the gas phase. At the same time, the energy, radiation, magnetic, and electrical characteristics of excited molecules, which are of interest for different physicochemical applications, must be determined and predicted at the experimental (spectral) level of accuracy in a broad range of electron vibrational and rotational excitations. This problem cannot be solved within spectroscopy's traditional adiabatic approximation, since a large number of intramolecular interactions (so-called perturbations) inevitably distorts not only the regular energy structure of different levels but he nodal structure of the corresponding wave functions as well. The most accurate solution to both direct and inverse spectroscopic problems with respect to perturbed molecular states is based on constructing a reduced system of the coupled radial Schrödinger equations encountered in the quantum-mechanical modeling of the nonadiabatic interaction of electronic states. The nonadiabatic approach can be employed successfully only through the joint use of precision spectroscopic data and highly precise calculations of electronic structure. [ABSTRACT FROM AUTHOR]

In this paper, by introduction of pseudopotentials, the nonlocal symmetry is obtained for the Ablowitz–Kaup–Newell–Segur system, which is used to describe many physical phenomena in different applications. Together with some auxiliary variables, this kind of nonlocal symmetry can be localized to Lie point symmetry and the corresponding once finite symmetry transformation is calculated for both the original system and the prolonged system. Furthermore, the nth finite symmetry transformation represented in terms of determinant and exact solutions are derived. [ABSTRACT FROM AUTHOR]

A first principles study of the electronic structure of strained Ge is carried out within the framework of plane wave pseudopotential density functional theory (DFT) combined with the GW approximation to the self-energy. Systematic investigations of the variations of high symmetry quasiparticle gaps over for a range of pseudopotential approximations are carried out. It is found that the quasiparticle corrections can be at least as sensitive to the choice of DFT approximation as to pseudopotential generation scheme, level of core-valence interaction, and pseudopotential electronic configuration. The latter can be decisive in the resulting prediction of the band gap transition strain, as the magnitudes of exchange and correlation terms involved in the quasiparticle corrections at the conduction valleys are largely determined by the arrangement of orbitals at those regions of the bandstructure, which in turn is determined by the pseudized electronic configuration. [ABSTRACT FROM AUTHOR]

Based on a pseudopotential approach under the virtual crystal approximation that includes the effect of compositional disorder, the optical lattice vibration frequencies and polaron related parameters in zinc-blende Ga x In 1−x P have been studied. Our findings showed generally reasonably good accord with data in the literature. Other case, our results are predictions. The composition dependence of longitudinal optical (LO) and transverse optical (TO) phonon modes, LO-TO splittings, Frӧhlich coupling parameter, Debye temperature of LO phonon frequency, and polaron effective mass has been analyzed and discussed. While a non-monotonic behavior has been noticed for the LO and TO phonon frequencies versus Ga concentration x, a monotonic behavior has been observed for the rest of the features of interest. The information derived from this investigation may be useful for optoelectronic technological applications. [ABSTRACT FROM AUTHOR]

The dependence on hydrostatic pressure of the electronic and optical properties of zinc-blende AlSb semiconducting material in the pressure range of 0–20 kbar has been reported using a pseudopotential approach. At zero pressure, our findings showed that the electron and heavy hole effective masses are 0.11 and 0.38 m 0 , respectively. Moreover, our results yielded values of 3.3289 and 11.08 for refractive index and high frequency dielectric constant, respectively. These results are found to be in good accord with experiment. Upon compression, all physical parameters of interest showed a monotonic behavior. The pressure-induced energy shifts for the optical transition related to band-gaps indicated that AlSb remains an indirect (Г-X) band-gap semiconductor at pressures from 0 to 20 kbar. The trend in all features of interest versus pressure has been presented and discussed. It is found that the lattice parameter is reduced from 0.61355 to 0.60705 nm when pressure is raised from 0 to 20 kbar. The present investigation may be useful for mid-infrared lasers applications, detectors and communication devices. [ABSTRACT FROM AUTHOR]

We report a study of optical properties, namely the optical band gaps, the refractive index and the high-frequency and static dielectric constants of zinc-blende AlxIn1-xP ternary semiconductor alloys. The calculations are mainly based on the pseudopotential approach under a modified virtual crystal approximation that takes into account the effect of compositional disorder. The composition dependence of the band parameters of interest has been examined and discussed. The material system under consideration is found to be a direct band-gap semiconductor within the composition range 0 ≤ x ≤ 0.4 and an indirect band-gap semiconductor for 0.4 < x ≤ 1. A good agreement is noticed between our results and the available experimental and theoretical data quoted in the literature. [ABSTRACT FROM AUTHOR]

The composition dependence of direct and indirect band gap energies, anti-symmetric gap, valence band width, refractive index and high-frequency and static dielectric constants has been investigated for GaAs 1-x N x ternary semiconductor alloys with the zinc-blende crystal structure over the whole nitrogen concentration range (x from 0 to 1). The calculations are mainly based on the pseudopotential approach within the virtual crystal approximation. The variation of band-gaps versus nitrogen content show important bowing parameters. Trends in ionicity have been discussed in terms of the anti-symmetric gap. The alloy concentration dependence of the optical parameters of interest is found to be highly nonlinear. [ABSTRACT FROM AUTHOR]

The strongly luminescent and highly oxygen-sensitive Tb(III) complex [{(MeMeArO) 3 tacn}TbIII(THF)] (denoted hereafter as [ 1 Tb THF]) was studied with density functional theory (DFT) and wavefunction-based ab initio electronic structure methods combined with Tb relativistic ab initio pseudopotentials. The optimized geometries as well as the calculated UV–vis absorption spectra at the DFT level agree well with the available experimental data. The calculated vertical S 0 */5D 4 → S 0 */7F J (ligand/Tb3+ states) emission energies for J = 0–6 at the RSPT2//CASSCF level including spin-orbit corrections are 475, 511, 549, 583, 614, 638, and 644 nm, respectively, and are lower by 15, 36, 39, 39, 39, 35, and 35 nm, respectively, than the corresponding experimental values. The luminescence quenching mechanism of [ 1 Tb THF] in presence of O 2 was investigated. RSPT2//CASSCF calculations for [ 1 Tb THF]·O 2 indicate that the S 0 */7F J (J = 0–6)/1O 2 (1Δ g or 1Σ+ g) states (ligand/Tb3+/O 2 states) are energetically more stable than the emission states S 0 */5D J (J = 0–4)/3O 2 (3Σ- g). Therefore, after initial photo excitation of the ligand and subsequent energy transfer to the Tb3+ ion, the energy will be further transferred to O 2 leading to the observed luminescence quenching of [ 1 Tb THF] in air. A comparison is made to [ 1 Sm THF]·O 2 which shows a significantly smaller luminescence quantum yield and no oxygen quenching. [Display omitted] • Quantum chemical study of the complex [{(MeMeArO) 3 tacn}TbIII(THF)] ([ 1 Tb THF]). • Structures, UV–vis absorption and emission spectra agree with experimental data. • Explanation why [ 1 Tb THF] shows strong luminescence and O 2 quenching. • Explanation why [ 1 Sm THF] shows weak luminescence and no O 2 quenching. [ABSTRACT FROM AUTHOR]

Ab initio investigation has been performed for the strontium hydride cation SrH + using a standard quantum chemistry approach. It is based on the pseudopotentials for atomic core representations, Gaussian basis sets, as well as with full configuration interaction calculations. A diabatisation procedure based on the effective hamiltonian theory and an effective metric is used to produce the quasi-diabatic potential energy. Adiabatic and quasi-diabatic potential energy curves and their spectroscopic parameters for the ground and many excited electronic states of 1,3Σ+, 1,3Π, and 1,3Δ symmetries have been determined. Their predicted accuracy is discussed by comparing our well depths and equilibrium positions with the available experimental and theoretical results. Moreover, we localized and analyzed numerous avoided crossings between the electronic states of 1,3Σ+ and 1,3Π symmetries. The correction of the electron affinity of the H atom is also considered, for the 1-101Σ+ electronic states, to improve the accuracy of the adiabatic potential energies of these states. In addition, we calculated the dipole moments, for a wide range of internuclear distances in both diabatic and quasi-diabatic representations. The adiabatic permanent dipole moments for the 101Σ+ electronic states revealed ionic characters related to electron transfer and yields both SrH(+) and Sr(+)H arrangements. The transition dipole moments between neighbor electronic states revealed many peaks around the avoided crossing positions. [ABSTRACT FROM AUTHOR]

The importance of the semi-core-valence interaction for plane-wave pseudopotential calculations with exact exchange is investigated for group IVA, IIIA-VA, and IIB-VIA semiconductors. Results for different valence spaces, either omitting or including the semi-core d- and/or the semi-core sp-states, are compared with full-potential LAPW all-electron data. It is found that for group IIB, IIIA, and IVA elements only the valence space including all semi-core states leads to accurate band structures. In fact, no real improvement over the minimum valence space is obtained for group IIIA and IVA elements, if only the semi-core d-states are taken into account. The particular relevance of the semi-core sp-states arises from the nonlocality of the exact exchange, which makes the exchange potential in the valence region sensitive to orbital structures located in the semi-core region (such as the nodes of the valence states). In contrast, even the valence space without any semi-core states yields very accurate results in the case of group VA elements, indicating the onset of the decoupling of the M-shell from the valence states. To deal with valence spaces including all semi-core states a proper construction of pseudopotentials is essential. While usually the energetically lowest state in the valence space is utilized to generate the pseudopotential for the corresponding angular momentum, it is shown here that this procedure can induce significant errors, when applied in the presence of semi-core states. Accurate results are only obtained, if the pseudopotentials are generated from the (occupied) valence states (under the constraint that the corresponding pseudoorbitals have one node), the reason being that the norm-conservation of the valence states is more important for the electronic structure of the bulk than that of the semi-core states. As a byproduct, it is shown that highly accurate pseudopotential results can also be obtained for solid Ne. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The structural, dynamical and thermodynamical properties of the yttrium pnictides YN, YP, As and YSb compounds in the NaCl (B1) stable phase and the CsCl (B2) unstable phase structures are studied by performing ab initio calculations with the help of the generalized gradient approximation (GGA). The computed lattice parameters; lattice constants, static bulk modulus and corresponding first-order pressure derivative of the bulk modulus are obtained in the two structures NaCl and CsCl and compared with other theoretical and experimental values. The transition pressure from B1 type to B2 type phases is presented and it is about 171, 72, 75 and 34 GPa for YN, YP, YAs and YSb compounds respectively. To obtain the dispersion relation curves and density of states we used the linear-response approach to the density functional theory in both structures. The values of phonon frequencies are used to obtain the thermodynamic quantities such as entropy and heat capacity as function of temperature at different pressures. [ABSTRACT FROM AUTHOR]

We summarize life and work on nonideal plasma thermodynamics of the late Fazylkhan Baimbetov. Analyzing Baimbetovs method of pseudo potentials we develop several extensions. First we optimize the parameter choice by comparing with recent exact results for thermodynamics. We compare the result of the pseudopotential method with the available exact results, check the formulae for stability and show generalizations of the pseudo potentials and extensions for higher densities. In particular we demonstrate how the introduction of the full Kelbg potential and the Debye-Kaklyugin methods of suppression of high plasma wave modes allows to include higher orders in density up to Wigner-type lattice-like contributions. We show how a new pseudopotential for the free charges can be combined with HNC integral equations. In conclusion we find that the analytical results obtained by Baimbetovs method are, with some improvements, in good overall agreement with available exact results. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The all-electron-derived pseudopotential (AEPP) scheme recently proposed has been extended to simulate non-spherical frozen-core entities. As an application, the embedding of an iodine anion in a cage of frozen water molecules is considered. It is shown that the AEPP approach which is intermediate between a pseudopotential and an all-electron frozen-core treatment has a good cost/performance ratio for the evaluation of the I−polarisability. [ABSTRACT FROM PUBLISHER]

Based on a pseudopotential approach under the virtual-crystal approximation, the electron and positron band structures and their derived properties have been investigated for zinc-blende Al x In 1− x Sb ternary semiconductor alloys. The effect of compositional disorder on electron and positron band structures has been examined and discussed. Moreover, the differences and the similarities between electron and positron characteristics in the material system of interest have been analyzed. The present study reveals possibilities for the investigation of the positron annihilation in Al x In 1− x Sb. [ABSTRACT FROM AUTHOR]

The effects of exchange–correlation (XC) and pseudopotential types on the density functional theory-driven prediction of the thermal conductivity of isotopically pure silicon are studied. The thermal conductivity is predicted by considering three-phonon scattering processes and a full solution of the Boltzmann transport equation. The LDA, PBE, PBEsol, and PW91 XCs predict thermal conductivities between 127 and 148 W/m K at a temperature of 300 K, which is an under-prediction of the experimental value of 153 W/m K by 3–17%. The BLYP XC predicts a thermal conductivity of 172 W/m K, an over-prediction of 12%. [ABSTRACT FROM AUTHOR]