Combination Of Atomic Orbitals Method Research Articles

Simulating and Analyzing the Electronic Structure of a Spherical Amorphous SiO2 Nanoparticle of Finite Radius

This study focuses on the electronic structure and properties of amorphous SiO2 nanoparticle with a radius of 18 Å using Density Functional Theory and the Orthogonalized Linear Combination of Atomic Orbital method. Through employing appropriate statistical techniques, three distinct models (I, II, and III) of amorphous SiO2 nanoparticle with an 18 Å radius are generated based on the continuous random network structure incorporating periodic boundaries. The calculated Total Density of States and Partial Density of States reveal insights into the electronic interactions within the nanoparticle. The band gap values are assessed at both less accurate and more accurate potentials such that the band gap increases from 2 eV to 4.2 eV with higher potentials for Model I, where surface atoms has dangling bonds stabilized by hydrogen atoms. Model II, consisting of all surface silicon atoms bonded to four oxygen atoms, exhibits a band gap of 1 eV, increasing to 1.8 eV with higher potentials. Model III, saturated with hydrogen atoms, shows a band gap of 4 eV, decreasing to 3.75 eV at higher potentials. The introduction of the more accurate potential serves to minimize the gap states initially observed with the less accurate potential. The electronic structure calculations provide crucial information for understanding the electronic interactions within the amorphous SiO2 nanoparticle with implications for their applications in various fields such as biomedicine, catalysis, electronics, and nanotechnology.

First-principles calculations to investigate structural, electronic, optical and elastic properties of α-Ca3N2

The optoelectronic industry, which has become a cornerstone, requires a semiconductor compound to function as a sustainable and green energy source. In this connection, the present study provides a systematic approach to examine the electronic and optical properties of α-Ca3N2 using the linear combination of atomic orbitals method. The xc-functional BECKE-PBE gives the best results for electronic properties by describing the band gap correctly. The dispersion curve shows that α-Ca3N2 is a semiconductor with an indirect band gap of 1.33 eV along the H-Γ direction. Effective masses of electrons and holes are calculated at the peak of the lowest conduction band and highest valence band, along the Γ- direction. Calculation for optical properties has been performed using coupled-perturbed Hartree-Fock scheme for static values and phonon spectrum calculations are performed for dynamic dielectric functions. Further, frequency dependent electron loss function and reflectivity are determined from the dielectric functions. The elastic constants are estimated and elastic moduli are determined. Bulk modulus of 80.6 GPa and Poisson’s ratio of 0.275 reveals that α-Ca3N2 is a hard and ductile material. The characteristic properties of α-Ca3N2 make it a suitable candidate for optoelectronic applications.

Correspondence between the surface integral and linear combination of atomic orbitals methods for ionic-covalent interactions in mutual neutralization processes involving H−/D−

The surface integral method for estimating ionic-covalent interactions in diatomic systems been successful in producing cross sections for mutual neutralization (MN) in reasonable agreement with experimental results for branching fractions between final states in systems such as ${\mathrm{O}}^{+}\text{/}{\mathrm{O}}^{\ensuremath{-}}$ and ${\mathrm{N}}^{+}\text{/}{\mathrm{O}}^{\ensuremath{-}}$. However, for simpler cases of MN involving ${\mathrm{H}}^{\ensuremath{-}}$ or ${\mathrm{D}}^{\ensuremath{-}}$, such as ${\mathrm{Li}}^{+}\text{/}{\mathrm{D}}^{\ensuremath{-}}$ and ${\mathrm{Na}}^{+}\text{/}{\mathrm{D}}^{\ensuremath{-}}$, it has not produced results that are in agreement with experiments and other theoretical calculations; in particular, for ${\mathrm{Li}}^{+}\text{/}{\mathrm{D}}^{\ensuremath{-}}$ calculations predict the wrong ordering of importance of final channels, including the incorrect most populated channel. The reason for this anomaly is investigated, and a leading constant to the asymptotic ${\mathrm{H}}^{\ensuremath{-}}$ wave function is found that is different by roughly a factor of $1\text{/}\sqrt{2}$ from that which has been used in previous calculations with the surface integral method involving ${\mathrm{H}}^{\ensuremath{-}}$ or ${\mathrm{D}}^{\ensuremath{-}}$. With this correction, far better agreement with both experimental results and calculations with full quantum and linear combination of atomic orbitals (LCAO) methods is obtained. Further, it is shown that the surface integral method and LCAO methods have the same asymptotic behavior, in contrast to previous claims. This result suggests the surface integral method, which is comparatively easy to calculate, has greater potential for estimating MN processes than earlier comparisons had suggested.

First-principles characterization of the electronic properties of h-BN layers

We model the two-dimensional h-BN layers to investigate the electronic properties. The monolayer and bilayer configurations are considered for the 2D h-BN. The bilayers are constructed in the AAʹ and AB stackings. The first-principles calculations using periodic linear combination of atomic orbitals method within the framework of density functional theory are attempted. The lattice constants and interlayer distances are relaxed to predict preferred structures. The electronic band structure, density of states and the bandgap are presented and compared. Current results agree well with the reported experimental findings.

Theoretical insight into electronic and optical behaviour of H-adsorbed Zn-terminated Zn3N2-(100)-non-polar surface

Present paper deals with the study of electronic and optical behaviour of a II3-V2 group semiconductor compound Zn3N2 and corresponding significant alterations, that are realised after H-adsorption on its (100) non-polar surface. Calculations are performed applying the linear combination of atomic orbitals method. The relative stability of H-adsorbed systems represents the adsorption to be energetically favourable, indicating possible applications in H-storage devices. A direct electronic band gap of 1.59 eV at gamma point is reported, which is further converted into conducting and again semiconducting for slab and adsorbed configurations, respectively. This tuning of the band gap is very important outcome that may emerge new possibilities in optoelectronic field. Further, favourable alterations are perceived in optical behaviour as well, allowing more absorption possibilities in the optimum range of solar radiations. Consequently, efficiencies are supposed to get enhanced.

Ab initio study of structural properties of MgxCd1−xX(X = S, Se, Te) alloys

In the current research, the structural parameters of MgxCd1−xX (X = S, Se, Te) ternary semiconductor compounds are determined. Structures of binary compounds are also defined, using the computational approach in zinc blende (B3) structure. For determination of structural parameters, the first principles calculations for energy optimization have been done. As the concentration of Mg dopant goes up, the parameter lattice constant and bulk modulus decreases. The Linear Combination of Atomic Orbital method was used within DFT using CRYSTAL code. The Kohn-Sham Hamiltonian was being constructed using HYBRID B3LYP scheme. The structural parameters are studied in terms of bulk modulus and lattice constant. All the observations, graphs and obtained values are in good coordination with the previously done work.

Electronic and elastic properties of ternary fluoro-perovskite RbCaF3

We present the electronic and elastic properties of cubic perovskite type RbCaF3 computed using linear combination of atomic orbitals method within the framework of density functional theory (DFT). We have performed ab-initio calculations using the hybrid approach of Hartree-Fock and DFT namely, B3LYP (Becke’s 3 parameter functional combined with the nonlocal correlation functional of Lee-Yang-Parr) to determine the electronic response of Rb based cubic perovskite. In addition, we have computed elastic constants, bulk modulus, shear modulus, Young’s modulus and elastic anisotropes of RbCaF3. The results are found to be consistent with previously reported studies. The studied perovskite compound is mechanically stable, brittle in nature and show large elastic anisotropy. The band structure calculations reveal that RbCaF3 possesses indirect band gap with valence band maximum at R point and the conduction band minimum at the Γ point of the irreducible Brillouin zone.

Influence of Te doping in titanium dichalcogenides: LCAO calculations and Compton spectroscopy

Role of Te doping in titanium disulfide using linear combination of atomic orbitals method and Compton spectroscopy is reported. The theoretical Compton profiles (CPs) of TiSTe derived using various exchange and correlation potentials like Perdew-Burke-Ernzerhof, Perdew-Wang generalized gradient approximation and von Barth-Hedin (VBH) are compared with corresponding experimental CP to check the applicability of considered potentials. From the total and partial density of states, we observe that doping of Te at S site vanishes the narrow band gap of TiS2 leading to metallic character of TiSTe. A good agreement between experimental and VBH potential based CP of TiSTe shows better performance of VBH approximation in this mixed metal-like dichalcogenide.

Structural, electronic, bonding and optical properties of LiBaPO4: A comparative study of monoclinic and trigonal phases

Crystal structure, electronic, bonding and optical properties of monoclinic and trigonal phases of LiBaPO4 compound have been explored using the density functional theory based orthogonalized linear combination of atomic orbitals method. The outcomes of band structure and density of states reveal the insulating direct band gap (E g = 4.62 eV) and semiconducting indirect band gap (E g = 1.12 eV) natures of monoclinic and trigonal phases respectively. The highest bond order and shortest bond length of P–O bond disclose its highest strength over Ba–O and Li–O bonds in both phases of LiBaPO4. with %BO values of 53.20 and 59.34 in M-LiBaPO4 and T-LiBaPO4 respectively. Optical properties in the form of dielectric function, refractive index, optical conductivity and electron energy loss function have been comprehensively described. Dielectric studies demonstrate that the trigonal phase may find its use as a photovoltaic material for solar cell applications.

First-principles LCAO study of the low- and room-temperature phases of CdPS3

The electronic and atomic structure of a bulk 2D layered van-der-Waals compound CdPS3 was studied in the low (R3) and room (C2/m) temperature phases using first-principles calculations within the periodic linear combination of atomic orbitals method with hybrid meta exchange-correlation M06 functional. The calculation results reproduce well the experimental crystallographic parameters. The value of the indirect band gap Eg = 3.4 eV for the room-temperature monoclinic C2/m phase is close to the experimental one, while the indirect band gap Eg = 3.3 eV was predicted for the low-temperature trigonal R3 phase. The effect of hydrostatic pressure on the band gap in both phases was studied in the pressure range from 0 to 40 GPa. In both cases, the pressure dependence of the band gap passes through a maximum, but at different pressures. In the R3 phase, the band gap reaches its maximum value of ∼4 eV at ∼30 GPa, whereas in the C2/m phase, the maximum value of ∼3.6 eV is reached already at ∼8 GPa.

First-principles structural, electronic, optical and bonding properties of scandium-based ternary indide system Sc5T2In4 (T = Ni, Pd, Pt)

The structural, electronic and optical properties of rare-earth, scandium-based compounds within the family of RE5-T2-In4 (T = Ni, Pd, Pt) intermetallics are calculated by using density functional theory-based orthogonalized linear combination of atomic orbitals method. The studied compounds crystallize in orthorhombic structure with space group Pbam (No. 55). The electronic properties exhibit conducting features of all three compounds. Charge transfer and crystal strength analysis were carried out by computing bond order and effective charge. Regarding optical properties the complex dielectric function, optical conductivity and electron energy loss function have been assessed. All the three compounds demonstrate optically anisotropic behaviour for energy values up to 7.0 eV and turned towards isotropic nature at higher energy (>7.0 eV). Optical conductivity spectra designate that the compounds are optically active for visible to UV light. Two major peaks are observed in energy loss spectra, at 13.2 and 32.6 eV, which correspond to plasmonic resonance points. The interatomic bonding characteristics between distinct pair of atoms within each compound have also been elaborated in comprehensive manner.

Discontinuous Galerkin discretization for quantum simulation of chemistry

All-electron electronic structure methods based on the linear combination of atomic orbitals method with Gaussian basis set discretization offer a well established, compact representation that forms much of the foundation of modern correlated quantum chemistry calculations—on both classical and quantum computers. Despite their ability to describe essential physics with relatively few basis functions, these representations can suffer from a quartic growth of the number of integrals. Recent results have shown that, for some quantum and classical algorithms, moving to representations with diagonal two-body operators can result in dramatically lower asymptotic costs, even if the number of functions required increases significantly. We introduce a way to interpolate between the two regimes in a systematic and controllable manner, such that the number of functions is minimized while maintaining a block-diagonal structure of the two-body operator and desirable properties of an original, primitive basis. Techniques are analyzed for leveraging the structure of this new representation on quantum computers. Empirical results for hydrogen chains suggest a scaling improvement from O(N4.5) in molecular orbital representations to O(N2.6) in our representation for quantum evolution in a fault-tolerant setting, and exhibit a constant factor crossover at 15 to 20 atoms. Moreover, we test these methods using modern density matrix renormalization group methods classically, and achieve excellent accuracy with respect to the complete basis set limit with a speedup of 1–2 orders of magnitude with respect to using the primitive or Gaussian basis sets alone. These results suggest our representation provides significant cost reductions while maintaining accuracy relative to molecular orbital or strictly diagonal approaches for modest-sized systems in both classical and quantum computation for correlated systems.

Structural Properties of Scandium Chalcogenides via First Principle Calculations

Structural properties of scandium chalcogenides, whichused in the production of high-performance magnets, rechargeable batteries, alloys, catalysts, electronics and glasses,have investigated in NaCl (B1) structure using first principle calculations. Exchange correlation scheme of PBE and Becke has been used. The lattice constant and bulk modulus have found using linear combination of atomic orbital method within CRYSTAL06 code. The lattice constant and bulk modulus of ScS, ScSe, and ScTe are reported. The results are found to be compatible with the available experimental and theoretical data of the samples.

Origin of pressure-induced insulator-to-metal transition in the van der Waals compound FePS3 from first-principles calculations.

Pressure-induced insulator-to-metal transition (IMT) has been studied in the van der Waals compound iron thiophosphate (FePS3 ) using first-principles calculations within the periodic linear combination of atomic orbitals method with hybrid Hartree-Fock-DFT B3LYP functional. Our calculations reproduce correctly the IMT at ∼15 GPa, which is accompanied by a reduction of the unit cell volume and of the vdW gap. We found from the detailed analysis of the projected density of states that the 3p states of phosphorus atoms contribute significantly at the bottom of the conduction band. As a result, the collapse of the band gap occurs due to changes in the electronic structure of FePS3 induced by relative displacements of phosphorus or sulfur atoms along the c-axis direction under pressure.

Computational analysis of strain-induced electronic and optical properties of Zn3As2

In this article, strain-induced electronic and optical properties of Zn3As2 are assessed applying linear combination of atomic orbitals method under the framework of density functional theory. We present the fundamental properties namely, energy band gap, density of states, real and imaginary parts of dielectric function and electronic loss function. Moreover, the plasmon frequency, effective mass of charge carriers, excitonic binding energy, refractive index and reflectivity are also presented. The characteristic values are found to lie in a favourable range and suggest suitability of Zn3As2 in solar energy applications. The results provide necessary input for the photovoltaic applications to the experimental researchers.

Study of KCaF3 and CsCaF3 Using Hybrids Density Functionals

In this paper we present the electronic and elastic properties of cubic perovskites KCaF3 and CsCaF3 using exchange and correlation operators of density functional theory within linear combination of atomic orbitals method. The band structure calculations show an indirect band gap exist in KCaF3 and CsCaF3 with valence band maximum at R point and the conduction band minimum at the Γ point of the irreducible Brillouin zone. The elastic properties such as elastic constants, bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio and anisotropy factor are obtained. The present calculations show that KCaF3 and RbCaF3 are elastically anisotropic and the B/G ratio indicates that KCaF3 passes ductile character and CsCaF3 shows brittle nature

Investigation of Structural Properties of a Ternary Semiconductor Compound SrxCd1-xO (x= 0.00, 0.25, 0.50, 0.75 and 1.00)

The present work is based upon the investigation of structural properties of technologically important compound SrxCd1-xO (x= 0.00, 0.25, 0.50, 0.75 and 1.00) of group II-VI semiconductors. The Linear Combination of Atomic Orbital method has been used within density functional theory as embodied in CRYSTAL code. The Hybrid scheme B3LYP is used for making the Kohn-Sham Hamiltonian. The effect of the composition on lattice constant, bulk modulus is investigated. The deviations of the lattice constant from the Vegard’s law were observed for three cases

Thermoelectric characterization of ZnSb by first-principles method

The thermoelectric properties of semiconducting compound ZnSb are studied using crystalline orbitals program based on the periodic linear combination of atomic orbitals method. The calculations are done under the framework of density functional theory. We calculate the electronic band structure and the density of states. The k-space eigenvalues are coupled with Boltzmann transport equations to calculate transport coefficients such as the Seebeck coefficient, power factor and electronic thermal conductivity under the constant relaxation time and the rigid band approximations. Effect of the scissor correction on the transport coefficients is examined. We have found that ZnSb behaves as n-type thermoelectric. A comparison with available measurements is done and a good agreement is found. The thermoelectric performance is compared with other materials by means of the electronic fitness function which suggests ZnSb to be a good thermoelectric material.

Tight-binding model for borophene and borophane

Starting from the simplified linear combination of atomic orbitals method in combination with first-principles calculations, we construct a tight-binding (TB) model in the two-centre approximation for borophene and hydrogenated borophene (borophane). The Slater and Koster approach is applied to calculate the TB Hamiltonian of these systems. We obtain expressions for the Hamiltonian and overlap matrix elements between different orbitals for the different atoms and present the SK coefficients in a nonorthogonal basis set. An anisotropic Dirac cone is found in the band structure of borophane. We derive a Dirac low-energy Hamiltonian and compare the Fermi velocities with that of graphene.

Compton scattering study of MnO2

ABSTRACTThe results of the Compton scattering study of MnO2 are presented in this paper. 241Am source based Gamma-ray Compton spectrometer is used for experimental measurement. The theoretical values of the electron momentum density distribution are evaluated by the Linear combination of atomic orbitals method within the framework of density functional theory and compared with the experimental data. The estimation of charge transfer in MnO2 using ionic model is also performed and it was found that there is a charge transfer of 1.5 electrons from the 4s state of Mn to the 2p state of O atoms.