Ground-state Total Energy Research Articles

First principle insight on Mn doped BeTe compound for optoelectronic and spintronic applications

The structural, electronic, optical, magnetic and thermoelectric (TE) features of pristine and Mn doped BeTe compound were computed by mean of FP-LAW method. Magnetic stability at various doping concentrations in ferromagnetic (FM) ordering is investigated by minimizing the total ground state energies. A semiconductor behavior is predicated for BeTe and Be1−xMnxTe (X = 6.25, 12.5, 18.75, 25%) because of the fact that spin-up and spin-dn show semiconductor character with direct band gap (Eg). The total and partial density of states of resultant compound have also been calculated. Furthermore, the dilute magnetic semiconductors (DMS) have been considered as the potential candidate to be used in spintronics devices. The magnetic moment of Be1−xMnxTe (X = 6.25, 12.5, 18.75, 25%) has been studied by increasing the concentration of Mn atoms. The contribution of the Mn atoms is significant in the total magnetic moment of resultant alloys, while it is minor in Be and Te. Moreover, the optical features revealed the maximum absorption of light in visible to UV span of electromagnetic spectrum which makes it a potential candidate for optoelectronic applications. Outcome suggest that Mn doped BeTe is an interesting candidates for various technological applications.

Quantum Proton Effects from Density Matrix Renormalization Group Calculations.

We recently introduced [J. Chem. Phys. 2020, 152, 204103] the nuclear-electronic all-particle density matrix renormalization group (NEAP-DMRG) method to solve the molecular Schrödinger equation, based on a stochastically optimized orbital basis, without invoking the Born-Oppenheimer approximation. In this work, we combine the DMRG method with the nuclear-electronic Hartree-Fock (NEHF-DMRG) approach, treating nuclei and electrons on the same footing. Inter- and intraspecies correlations are described within the DMRG method without truncating the excitation degree of the full configuration interaction wave function. We extend the concept of orbital entanglement and mutual information to nuclear-electronic wave functions and demonstrate that they are reliable metrics to detect strong correlation effects. We apply the NEHF-DMRG method to the HeHHe+ molecular ion, to obtain accurate proton densities, ground-state total energies, and vibrational transition frequencies by comparison with state-of-the-art data obtained with grid-based approaches and modern configuration interaction methods. For HCN, we improve on the accuracy of the latter approaches with respect to both the ground-state absolute energy and proton density, which is a major challenge for multireference nuclear-electronic state-of-the-art methods.

The Analytical Effects of a Hydrostatic Pressure on the Ground State Energy of GaAs Quantum Dot at Low-Temperature: Algebraic Method

This analytical study focused on discussing the collective effects of hydrostatic pressure and temperature on the ground state energy for two electrons trapped in GaAs parabolic quantum dot in the presence of a magnetic field using the effective mass approximation. The electronic interaction was approximated by the Johnson-Payne potential model, where its parameters were carefully chosen to match the Coulomb interaction. It is noted that the ground state energy decreases with an increment in pressure while it increases linearly slightly with increasing temperature. As is customary, it was found that ground state energy decreases with increasing dot size and reach its bulk value as the dot becomes wider. Among the most prominent notes related to this study were as follows: (i) The largest contribution to the total ground state energy is caused by the relative motion since the effect of pressure on this part is more pronounced than the part of the center of mass that often does not feel the presence of pressure. (ii) Ground state energy shows temperature insensitivity while pressure exerts a tangible effect on the ground state energy in the strong magnetic field confinement. (iii) The effect of temperature on the ground state energy is always the opposite of the pressure effect. (iv) With regard to the increase in pressure, it was found that it reduces the electron separation (r), therefore the ground state energy decreases in the presence of the harmonic interaction that is directly proportional to the square of r, but compared to previous works mentioned in the literature, energy showed increased behavior because Coulomb's interaction is inversely proportional to the electron separation. (v) In the region of weak confinement (R>aB*), the effect of pressure on ground state energy becomes neglected, while this effect becomes noticeable in the region of ??strong confinement (R<aB*). Keywords: Quantum Dots, Hydrostatic Pressure, Harmonic e-e Interaction.

The Analytical Effects of a Hydrostatic Pressure on the Ground State Energy of GaAs Quantum Dot at Low-Temperature: Algebraic Method

This analytical study focused on discussing the collective effects of hydrostatic pressure and temperature on the ground state energy for two electrons trapped in GaAs parabolic quantum dot in the presence of a magnetic field using the effective mass approximation. The electronic interaction was approximated by the Johnson--Payne potential model, where its parameters were carefully chosen to match the Coulomb interaction. It is noted that the ground state energy decreases with an increment in pressure while it increases linearly slightly with increasing temperature. As is customary, it was found that ground state energy decreases with increasing dot size and reach its bulk value as the dot becomes wider. Among the most prominent notes related to this study were as follows: (i) The largest contribution to the total ground state energy is caused by the relative motion since the effect of pressure on this part is more pronounced than the part of the center of mass that often does not feel the presence of pressure. (ii) Ground state energy shows temperature insensitivity while pressure exerts a tangible effect on the ground state energy in the strong magnetic field confinement. (iii) The effect of temperature on the ground state energy is always the opposite of the pressure effect. (iv) With regard to the increase in pressure, it was found that it reduces the electron separation (r), therefore the ground state energy decreases in the presence of the harmonic interaction that is directly proportional to the square of r, but compared to previous works mentioned in the literature, energy showed increased behavior because Coulomb's interaction is inversely proportional to the electron separation. (v) In the region of weak confinement (R>a_B*), the effect of pressure on ground state energy becomes neglected, while this effect becomes noticeable in the region of strong confinement (R<a_B*). Keywords: Quantum Dots, Hydrostatic Pressure, Harmonic e-e Interaction.

Incorporating Sulfur Atoms into Palladium Catalysts by Reactive Metal–Support Interaction for Selective Hydrogenation

Incorporating Sulfur Atoms into Palladium Catalysts by Reactive Metal–Support Interaction for Selective Hydrogenation

Accurate total energies from the adiabatic-connection fluctuation-dissipation theorem

In the context of inhomogeneous one-dimensional finite systems, recent numerical advances [Phys. Rev. B 103, 125155 (2021)] allow us to compute the exact coupling-constant dependent exchange-correlation kernel $f^\lambda_\text{xc}(x,x',\omega)$ within linear response time-dependent density functional theory. This permits an improved understanding of ground-state total energies derived from the adiabatic-connection fluctuation-dissipation theorem (ACFDT). We consider both `one-shot' and `self-consistent' ACFDT calculations, and demonstrate that chemical accuracy is reliably preserved when the frequency dependence in the exact functional $f_\text{xc}[n](\omega=0)$ is neglected. This performance is understood on the grounds that the exact $f_\text{xc}[n]$ varies slowly over the most relevant $\omega$ range (but not in general), and hence the spatial structure in $f_\text{xc}[n](\omega=0)$ is able to largely remedy the principal issue in the present context: self-interaction (examined from the perspective of the exchange-correlation hole). Moreover, we find that the implicit orbitals contained within a self-consistent ACFDT calculation utilizing the adiabatic exact kernel $f_\text{xc}[n](\omega=0)$ are remarkably similar to the exact Kohn-Sham orbitals, thus further establishing that the majority of the physics required to capture the ground-state total energy resides in the spatial dependence of $f_\text{xc}[n]$ at $\omega = 0$.

Study of Zero Temperature Ground State Properties of the Repulsive Bose-Einstein Condensate in an Anharmonic Trap

The zero-temperature ground state properties of experimental 87Rb condensate are studied in a harmonic plus quartic trap [ V(r) = ½mω2r2 + λr4 ]. The anharmonic parameter (λ) is slowly tuned from harmonic to anharmonic. For each choice of λ, the many-particle Schrödinger equation is solved using the potential harmonic expansion method and determines the lowest effective many-body potential. We utilize the correlated two-body basis function, which keeps all possible two-body correlations. The use of van der Waals interaction gives realistic pictures. We calculate kinetic energy, trapping potential energy, interaction energy, and total ground state energy of the condensate in this confining potential, modelled experimentally. The motivation of the present study is to investigate the crucial dependency of the properties of an interacting quantum many-body system on λ. The average size of the condensate has also been calculated to observe how the stability of repulsive condensate depends on anharmonicity. In particular, our calculation presents a clear physical picture of the repulsive condensate in an anharmonic trap.

Two-dimensional electron gas in a non-Euclidean space

A charged particle in the presence of a perpendicular magnetic field is studied within the position-dependent translation operator formalism. We show that the solution of the resulting Schrödinger-like equation is mapped on the Morse oscillator, instead of the expected quantum harmonic oscillator. The anharmonicity that shows up naturally from the theory is analogous to corrections introduced by relativistic effects. Due to the non-Euclidean space, it is demonstrated that: (i) the degeneracy of the spin up and spin down levels is lifted and (ii) the Fermi energy and the total ground state energy of the two-dimensional electron gas is also modified.

Dipole and generalized oscillator strengths-dependent electronic properties of helium atoms immersed in a plasma

Atoms subjected to extreme environmental conditions are of fundamental importance due to the modification of their electronic properties. In this work, we study the helium atom when immersed in a plasma environment. In order to describe the plasma medium, we use two models when solving the Schrodinger equation in a restricted Hartree–Fock approach: the Debye–Huckel screened (DHS) potential and a more general exponential-cosine screened Coulomb (ECSC) potential. The plasma length parameter, $$\lambda $$ , in both model potentials characterizes the plasma screening effects which cause an increase or decrease in the electronic properties of the helium atom. We report results for the total electronic ground state energy, orbital energy, dipole oscillator strengths, generalized oscillator strengths (GOS), mean excitation energy, electrostatic dipole polarizability, and electronic stopping cross section. We find that the ECSC plasma model produces a less bound system than the DHS plasma model at the same value of the screening length, $$\lambda $$ . However, the ECSC model potential has a stronger dipole transition from the 1s to the 2p and 3p states than the DHS model potential. Also, the ECSC potential predicts a higher static dipole polarizability than the DHS model potential, with a consequent lower mean excitation energy. We also find a larger GOS for the ECSC than for the DHS for the same momentum transfer at the same value of the screening length, $$\lambda $$ . Consequently, the ECSC mode potential produces a larger electronic stopping cross section than the DHS for the same $$\lambda $$ and projectile velocity. In the limit of $$\lambda \rightarrow \infty $$ , we have excellent agreement with the free helium properties. These quantitative values for the electronic properties would be useful for the investigations of the atomic structure and collisions of helium atoms immersed in plasmas.

Artificial neural networks for the kinetic energy functional of non-interacting fermions.

A novel approach to find the fermionic non-interacting kinetic energy functional with chemical accuracy using machine learning techniques is presented. To that extent, we apply machine learning to an intermediate quantity rather than targeting the kinetic energy directly. We demonstrate the performance of the method for three model systems containing three and four electrons. The resulting kinetic energy functional remarkably accurately reproduces self-consistently the ground state electron density and total energy of reference Kohn-Sham calculations with an error of less than 5 mHa. This development opens a new avenue to advance orbital-free density functional theory by means of machine learning.

Electronic correlation, magnetic structure, and magnetotransport in few-layer CrI3

Using density functional theory combined with a Hubbard model (DFT+U ), the electronic band structure of CrI3 multilayers, both free-standing and enclosed between graphene contacts, is calculated. We show that the DFT+U approach, together with the 'around mean field' correction scheme, is able to describe the vertical magnetotransport in line with the experimental measurements of magnetoresistance in multi-layered CrI3 enclosed between graphene contacts. Moreover, by interpolating between different double-counting correction schemes, namely the 'around mean field' correction and the fully localized limit, we show their importance for describing both the band structure and the ground-state total energy consistently. Our description of the magnetic exchange interaction is compatible with the experimentally observed antiferromagnetic ground state in the bilayer CrI3 and the transition to a ferromagnetic arrangement in a small external magnetic field. Thus, using spin-polarized DFT+U with an 'around mean field' correction, a consistent overall picture is achieved.

First Principles Calculations of Electronic, Structural and Optical Properties of (PMMA–ZrO2–Au) and (PMMA–Al2O3–Au) Nanocomposites for Optoelectronics Applications

This study focuses on the quantum mechanical treatment of the geometrical optimization and the electronic structure problems of a nanomaterial PMMA and nanocomposites. The hybrid functional B3LYP/6-31G level of DFT is used to investigate four molecules divided into two groups, they are PMMA as an original basis molecule and (PMMA–Au), (PMMA–Al2O3–Au), (PMMA–ZrO2–Au) nanocomposites as the two group. The DFT calculations have been performed using Gaussian 09 package of programs. The geometrical optimization included both bonds in °A and angles in deg. The calculated electronic properties included the total energy, HOMO and LUMO energies, energy gap, ionization energy, electron affinity, electronegativity, electrochemical hardness, electronic softness and Electrophilic index. The geometrical optimization of PMMA and nanocomposites has been found in good agreement with the experimental data because of its relaxed geometrical parameters. One of the important results was obtain in this study, is the decreasing of the energy gap. This states that these nanocomposites are the nearest to semiconductor due to the both HOMO and LUMO levels become more adjacent. These consequences mention to construct new structures with new electronic properties. All nanocomposites need small energy to become cationdue to ionization potential is decrease with addition nanoparticles to the pure PMMA, but the electronic affinity is an increase with with addition nanoparticles to the pure PMMA. The total ground state energy of the PMMA have largest value of total energy compared for other nanocomposites, where ET decreased with addition nanoparticles to pure PMMA. The hardness decrease with addition nanoparticles to the pure PMMA, therefore all the nanocomposites are softer, and this reduces the resistance of a species to lose electrons. Good relax for the structures of the studied PMMA was obtained theoretically, in which, the angles C–C, C=O and C–H in pure PMMA are remain in the same ranges for other nanocomposites. In general, most of the studied nonocomposites direct electronic transition from the valence to conduction band with wave length lies in the range of solar spectrum. The obtained results showed that the (PMMA–ZrO2–Au) and (PMMA–Al2O3–Au) nanocomposites have huge applications in electronics and photo-electronics fields.

Ab-initio Calculations of the Structural, Electronic and Optical Properties of (Cdse)2 Clusters

The distinctive properties of cadmium selenide (CdSe) semiconductor situated it in a multitudinous number of applications. Although (CdSe)2 cluster has more than one isomer, the previous studies concentrated merely on one isomer. The goal of this study was to determine the various stable geometric structure isomers of (CdSe)2 clusters; also, structural, electronic, and optical properties of the stable isomers are investigated using density functional theory (DFT). First, geometry optimization calculations of the possible geometric isomers were carried out using the BroydenFletcher-Goldfarb-Shanno minimization (BFGS) algorithm. Total ground-state energy calculations showed that all the converged isomers have a high probability of existing in any experiment, relying on the implemented experimental technique. Twenty initial possible geometric structures were investigated, in which eleven isomers were converged. However, all of them are relaxed in the 2D planar geometry. The results showed that eleven possible stable isomers were disclosed, where the final structures of the converged isomers produced six different structures; three of them were not detected before. The rhombus structure was ascertained to be the most stable isomer followed by the trapezoidal structure of (CdSe)2. The isomers’ Cd-Se bond length are 2.50-2.74 A, and the average Cd-Se-Cd, Se-Cd-Se angles were 64.5o-123o and 56.3o-114.2o, respectively. Furthermore, the bond angles show that the selenium atom lone-pairs electrons are responsible for shifting the isomers’ structure from the linearity. The total ground-state energy differences were 0.00-1.82 eV. The calculated highest occupied molecular orbital (HOMO), and the lowest unoccupied molecular orbital (LUMO) gap of the isomers implied that the gap depends on the symmetrical geometry of the isomer. Furthermore, it was evident that the most stable isomers are accompanied with larger gaps. The HOMO-LUMO graphs demonstrated that HOMO orbitals were localized around the selenium atom, while LUMO orbitals were distributed around both cadmium and selenium atoms. The calculated absorption spectrum was unique for each isomer. The absorption edges for the isomers are ranging from 2.53 to 3.73 eV. The results show that the obtained absorption spectra peaks’ values (nm) are smaller compared to CdSe experimental results. (CdSe)2 clusters are very active that they straightforwardly react to produce larger clusters. Finally, the results of this study corroborate with previous computational studies.

A quantum Monte Carlo study of the structural and electronic properties of small boron clusters [formula omitted][formula omitted

Using diffusion quantum Monte Carlo, density functional theory, and Hartree–Fock methods, we investigate the structural and electronic properties of small neutral boron clusters with up to 13 atoms. We determine the lowest-lying energy structures, total ground-state energy, binding energy, dissociation energy, resonance energy, and investigate the impact of electron correlation on the stability of the clusters. The obtained results show agreement with available experimental and theoretical results. Moreover, analysis of the dissociation energy, the second difference in energy, and the resonance energy indicates that the clusters B3, B4, B8, and B10 are relatively more stable.

First-principles calculation of excited states of diatomic molecules: a benchmark for the Gutzwiller conjugate gradient minimisation method

We recently proposed the Gutzwiller conjugate gradient minimisation (GCGM) method for efficient and accurate calculation of the ground state total energy of molecular and bulk systems. The GCGM method is developed under the framework of Gutzwiller wave function but goes beyond the commonly adopted Gutzwiller approximation to improve the accuracy and flexibility in treating the correlation effects. In this conference proceeding, we benchmark the GCGM method with the calculation of excited state potential energy curves of three diatomic molecules, namely H2, N2, and O2. Our calculations demonstrate the flexibility and reasonable accuracy of the method.

First-principle calculation investigation of NbMoTaW based refractory high entropy alloys

Alloying is an effective method to strengthen high entropy alloys (HEAs). Unfortunately, most of the investigations focus on the perspective of experiments and few are available from the perspective of atomic and electrical scale such as electronic structure, energy band structure and charge density. In present work, first-principle calculation based on density functional theory was employed to calculate the ground state total energy, lattice parameters, elastic constants and polycrystal modulus of NbMoTaW and NbMoTaWV refractory high entropy alloys (RHEAs). The effects of V addition on the phase structure, elastic properties and electronic structure of NbMoTaW-based RHEAs were studied, respectively. V addition is helpful to improve the mechanical properties of NbMoTaW alloy according to the calculated value of shear modulus to bulk modulus, Cauchy pressure and Vickers hardness. Based on calculated energy band, electronic state density, charge density and charge density difference, V addition is found to shorten the pseudo-energy gap and enhance interaction force between Mo and W atoms. This tends to improve the mechanical properties of the alloy. The calculated results were in good agreement with the experimental data, demonstrating that the methods were effective in predicting the performance of RHEAs.

A Simple Monte Carlo Simulation For the Two Dimensional Attractive Hubbard Model

We use the Auxiliary Field Quantum Monte Carlo technique to perform a simple study of the two dimensional attractive Hubbard model and calculate the total ground state energy to compare with another technique in the literature for U = –4t. Our finite size extrapolated result corroborate the approximated lattice density-functional theory method for this value of U at half-filling. To stabilize the Auxiliary Field Quantum Monte Carlo algorithm one must resort to one of the two decomposition methods: the modified Grand-Schmidt decomposition and the singular value decomposition. Two characteristics like accuracy and total execution time were considered to compare the decomposition algorithms, and the results are presented bellow.

Ab initio investigation on Half-Heusler CoTiSi

We report band structural calculations on half-Heusler alloy CoTiSi using Korringa–Kohn–Rostoker method applied for various formalism of potential. Murnaghan equation of state is used to minimize ground state total energy and then equilibrium lattice parameter is estimated. From density of state (DOS), it is seen that the Fermi energy is not lying in the gap and a close inspection of DOSs at the Fermi level reveals the absence of gap around the Fermi level suggesting the absence of half-metallic nature and the same is also confirmed by electronic band structure diagram.

Efficient method for grand-canonical twist averaging in quantum Monte Carlo calculations

We introduce a simple but efficient method for grand-canonical twist averaging in quantum Monte Carlo calculations. By evaluating the thermodynamic grand potential instead of the ground state total energy, we greatly reduce the sampling errors caused by twist-dependent fluctuations in the particle number. We apply this method to the electron gas and to metallic lithium, aluminum, and solid atomic hydrogen. We show that, even when using a small number of twists, grand-canonical twist averaging of the grand potential produces better estimates of ground state energies than the widely used canonical twist-averaging approach.

Influence of defect pairs in Ga-based ordered defect compounds: a hybrid density functional study

In the present paper, density functional theory (DFT) based calculations have been performed to predict the stability, electronic, and optical properties of Ga-rich ordered defect compounds (ODCs). The calculated lattice constants, bulk modulus, their pressure derivatives, and optical constants show good agreement with available experimental data. The hybrid exchange correlations functional have been considered to calculate ground state total energy and energy band gap of the material. The calculated formation energy of ODCs comes smaller than pure CuGaSe2 (CGS). Our calculated optical absorption coefficients indicate that the energy band gap of ODCs can be tuned by changing the number of donor–acceptor defect pairs ([Formula: see text]). The band offset has been calculated to understand the reason of band gap alteration while the number of defect pair changes. Our results may be helpful for other experiments to further improve the performance of ODCs.