Exchange-correlation Potential Research Articles

Effects of oxygen vacancies on the structural, electronic, and optical properties of the photocatalytic InTaO4 compound

We conducted first-principles calculations based on density functional theory to investigate the impact of the oxygen vacancies on the structural, electronic, and optical properties of the InTaO4 compound. The latter is a famous photocatalytic semiconductor with its optical absorption in the visible range being an object of controversial interpretations. The presence of two types of isolated oxygen vacancies, O1 and O2, occupying 4g(1) and 4g(2) Wyckoff positions respectively, has been simulated within the frame of the supercell approach. Electronic structure and optical absorption (OA) have been calculated using the Becke-Johnson exchange-correlation potential. It is found that the presence of both types of vacancies generates defect states (DS) inside the band gap, primarily involving In-6s and O-2p states. The calculated valence-to-conduction-band band gap (4.25 eV) and DS-to-conduction-band band gap (2.5 eV) closely align with the experimentally determined OA edges for two onsets of InTaO4 absorption. The analysis of the calculated OA spectra leads to the conclusion that only O1 vacancy-induced absorption is consistent with the experimental OA, while O2 vacancy-induced absorption appears absent. This discrepancy probably arises from a higher concentration of O1 vacancies formed during crystal growth, attributed to the fact that the calculated defect formation energy of O1 vacancy is 0.258 eV lower compared to O2 vacancy. Consequently, the photocatalytic activity of InTaO4 is ascribed to intrinsic defects, primarily O1-type vacancies, though the influence of other defects cannot be entirely ruled out.

Crystal structure, stability, and transport properties of Li2BeAl and Li2BeGa Heusler alloys: a DFT study

In this study, the structural, elastic, electronic, and thermoelectric properties of full Li2BeAl and Li2BeGa Heusler alloys were explored using density functional and the Boltzmann transport theories. The GGA and HSE approximations have been used for the exchange–correlation potential. Results indicated that these two compounds are more energetically stable in the inverse Heusler structure. Additionally, both Li2BeAl and Li2BeGa Heusler alloys were found to be mechanically stable due to the positive values of the elastic constants. Also, the high values of the Young's modulus indicate that these compounds are stiff and exhibit a semi-metallic nature. The band gaps were determined to be 0.13 eV and − 0.22 eV for Li2BeAl and Li2BeGa alloys, respectively, using the GGA approximation. By employing the HSE hybrid functional, however, the band gap for Li2BeAl increased to 0.26 eV, and for Li2BeGa, it decreased to − 0.16 eV. Regarding thermoelectric properties, Seebeck coefficient, electrical conductivity, electronic and lattice thermal conductivities, power factor, and the figure of merit have been calculated for both Li2BeAl and Li2BeGa Heusler alloys at different temperatures. Seebeck coefficient in both alloys decreases with increasing the temperature and has the highest value at 300 K. Thermal conductivity and electrical conductivity increase with increasing the temperature, which confirms the intermetallic behavior of the Heusler alloys. The results obtained for both alloys show that n-type doping has better thermoelectric properties than p-type doping. The maximum value of the figure of merit (ZT) was obtained for n-type doping, which was 1.43 at 660 K for Li2BeAl and 0.39 at 1000 K for Li2BeGa alloy. The high values of ZT especially for electron-dopped Li2BeAl suggest the great potential of this material for use in thermoelectric devices. This study suggests that the proposed materials have potential applications in spintronic devices and thermoelectric materials due to their intermetallic character and effective thermoelectric coefficients.

Thermodynamic stability and vibrational properties of multi-alkali antimonides

Abstract Modern advances in generating ultrabright electron beams have unlocked unprecedented experimental advances based on synchrotron radiation. Current challenges lie in improving the quality of electron sources with novel photocathode materials such as alkali-based semiconductors. To unleash their potential, a detailed characterization and prediction of their fundamental properties is essential. In this work, we employ density functional theory combined with machine learning techniques integrated into the hiphive package to probe the thermodynamic stability of various alkali antimonide crystals, emphasizing the role of the approximations taken for the exchange-correlation potential. Our results reveal that the SCAN functional offers an optimal trade-off between accuracy and computational costs to describe the vibrational properties of these materials. Furthermore, it is found that systems with a higher concentration of Cs atoms exhibit enhanced anharmonicities, which are accurately predicted and characterized with the employed methodology.

Electron-photon exchange-correlation approximation for quantum-electrodynamical density-functional theory

Quantum-electrodynamical density-functional theory (QEDFT) provides a promising avenue for exploring complex light-matter interactions in optical cavities for real materials. Similar to conventional density-functional theory, the Kohn-Sham formulation of QEDFT needs approximations for the generally unknown exchange-correlation functional. In addition to the usual electron-electron exchange-correlation potential, an approximation for the electron-photon exchange-correlation potential is needed. A recent electron-photon exchange functional [C. Schäfer , ], derived from the equation of motion of the nonrelativistic Pauli-Fierz Hamiltonian, shows robust performance in one-dimensional systems across weak- and strong-coupling regimes. Yet, its performance in reproducing electron densities in higher dimensions remains unexplored. Here we consider this QEDFT functional approximation from one- to three-dimensional finite systems and across weak to strong light-matter couplings. The electron-photon exchange approximation provides excellent results in the ultrastrong-coupling regime. However, to ensure accuracy also in the weak-coupling regime across higher dimensions, we introduce a computationally efficient renormalization factor for the electron-photon exchange functional, which accounts for part of the electron-photon correlation contribution. These findings extend the applicability of photon-exchange-based functionals to realistic cavity-matter systems, fostering the field of cavity QED (quantum-electrodynamics) materials engineering. Published by the American Physical Society 2024

Novel Prediction Using TB-mBJ of Electronic Properties, Magnetic Exchange Couplings, and Half-Metallicity in CrCaSe Materials

In this study, we have performed investigations on the structural stability, elec-tronic band structures, magnetic exchange couplings, and half-metallic performance of CrxCa1-xSe materials using computational methods of density functional theory via GGA-WC, GGA-PBE and, TB-mBJ exchange-correlation potentials. The CrxCa1–xSe compounds are thermodynamically stable and synthesizable owing to their negative formation energies. The structural parameters of CrxCa1–xSe with GGA-WC and GGA-PBE approximations appear to be in excellent concordance compared to the experi-mental data and recent theoretical calculations. According to GGA-PBE and TB-mBJ calculations, the CrxCa1–xSe compounds revealed integral magnetic moments and a half-metallic behavior with better half-metallic gaps, and spin-polarization of 100%. The CrxCa1–xSe alloys appear to be better materials for use in spintronic devices.

Current density functional framework for spin-orbit coupling: Extension to periodic systems.

Spin-orbit coupling induces a current density in the ground state, which consequently requires a generalization for meta-generalized gradient approximations. That is, the exchange-correlation energy has to be constructed as an explicit functional of the current density, and a generalized kinetic energy density has to be formed to satisfy theoretical constraints. Herein, we generalize our previously presented formalism of spin-orbit current density functional theory [Holzer et al., J. Chem. Phys. 157, 204102 (2022)] to non-magnetic and magnetic periodic systems of arbitrary dimension. In addition to the ground-state exchange-correlation potential, analytical derivatives such as geometry gradients and stress tensors are implemented. The importance of the current density is assessed for band gaps, lattice constants, magnetic transitions, and Rashba splittings. In the latter, the impact of the current density may be larger than the deviation between different density functional approximations.

Analysis of structural, electronic and optical properties of Er-doped rock salt AlN using ab-initio calculations.

This investigation includes the structural and optoelectronic characteristics of both pure and Er-doped rock salt aluminium nitride (AlN). Upon introducing Er doping into the AlN host, the calculations reveal a rise in the atomic parameter. Incorporating Er into the system leads to enhancements in the static dielectric coefficient ɛ1(0), static reflectivity R(0), as well as static refractive index n(0), at zero frequency. After doping, the peaks of imaginary dielectric tensor, extinction coefficient and absorption coefficient shift towards lower energy levels. Various exchange correlation potentials are incorporated to compare the results of electronic and optical characteristics. We employed the full potential linearized augmented plane wave (FP-LAPW) approach with WIEN2k code in conjunction with the density functional theory (DFT). To explore the optoelectronic characteristics of both pure as well as doped systems, three distinct exchange correlation potentials are utilized: the Perdew-Burke-Ernzerhof Generalized Gradient Approximation (PBE-GGA), Modified Becke Johnson Generalized Gradient Approximations (mBJ + GGA) and Hubbard potential (GGA + U).

Investigation of structural, magnetic, mechanical, electronic and thermal properties of new quaternary Heusler: KMgNZ (Z=O or S)

The structural stability as well as the mechanical, magnetoelectronic and thermal properties of the quaternary Heusler KMgNZ (Z = O or S) were studied using first principles approach based on the DFT implemented in Wien2k code. The exchange-correlation potential is treated by PBE-GGA. The calculated negative formation energies for both materials corroborate their thermodynamic stability. Moreover, the derived elastic constants support the mechanical stabilities of the latter compounds. On the other hand, the density of states of the studied materials shows that both compounds are half-metallic ferromagnets. The total magnetic moments for both compounds are mainly originated from N atom, and its integer value followed the Slater-Pauling rule. The calculated half-metallic gaps are found for two systems. The three-dimensional plots of different mechanical moduli exhibit that the bulk modulus is isotropic, whereas Young's modulus, Poisson's ratio and shear modulus of both compounds are highly anisotropic. The effects of temperature and pressure on the heat capacity, thermal expansion coefficient and Debye temperature are also studied.

DFT+U, TB-mBJ, and hybrid approaches: investigating electronic topology and magnetic properties in Sn-doped Co2TiGa

Cobalt-based Heusler compounds represent a new class of Heusler alloys which absorbed a lot of attention due to their performance in spintronics and magnetic devices. in this paper we have studied and analyzed the electronic structure and half-metallic ferromagnetic properties of Co2TiGa and Sn substituted at Ga site via the density functional theory (DFT) based first principle calculations with GGA-PBE, PBE+U, TB-MBJ exchange correlation potential and HSE06 approach. The band structure topology indicates that the parent ternary Heusler compound is ferromagnetic half-metallic with a half-metallic gap (band gap in the minority channel). The gap is increased according to the correction made on the exchange correlation potential. The half-metallic ferromagnetic behavior is confirmed by the total magnetizations which are very close to integrals Bohr magneton (1 μ B and 3μ B for Co2TiGa and Mn2TiGa0.5Sn0.5, respectively). The origin of half-metallic ferromagnetic is the p − d exchange and double-exchange interaction between the Co d-t2g states and neighboring Ti atom. The substitution effect on half-metallicity for Co2TiGa0.5 Sn0.5 was investigated in the tetragonal structure. The spontaneous magnetization obeyed the Slater-Pauling rule, indicating the Co2TiGa0.5 Sn0.5 is half-metal with 100% spin polarization.

A DFT approach to explore the structural, optoelectronic, mechanical, and thermoelectric attributes of lead-free RbInX3 (X = I, Br, Cl) halide perovskites for renewable energy applications

Halide perovskites are significant due to their versatility and high performance in optoelectronics and green technologies. This paper thoroughly investigates the structural, elastic, optoelectronic and transport characteristics of RbInX3 (X = I, Br, Cl) perovskites using density functional theory (DFT) embedded in Wein2K. Modified Becke Johnson as an exchange correlation potential is used to evaluate the physical characteristics. Structural stability is achieved with the tolerance factor and octahedral tilting along with the optimization curves. A metallic character is detected in RbInI3. However, the replacement of I with Br and Cl atoms results in an indirect band gap of 0.9 eV and 1.95 eV at (L-X) symmetry points, respectively. The elastic constants are utilized to determine the elastic parameters that ensure the structural stability of perovskites. Cauchy pressure and Poisson’s ratio indicate the ductile nature of all studied phases. The thermal behavior is evaluated through the computation of Debye temperature. Furthermore, an insight into the material’s interaction with electromagnetic radiation is accessed through the optical parameters. A high absorption at 1.49 eV for RbInI3, 1.65 for RbInBr3 and 2.57 for RbInCl3 show their potential for light emitting devices. The semi-classical Boltzmann theory is employed to compute thermoelectric properties, which show RbInI3, RbInBr3 and RbInCl3 possess high electrical conductivities of 3.068 ×1019 S m–1, 1.88 ×1019 S m–1 and 1.76 ×1019 S m–1 at 1200 K, respectively. The ZT value for RbInBr3 is 0.74 and RbInCl3 is 0.73, while RbInI3 exhibit the lowest ZT of 0.04 at 1200 K. The examined characteristics indicate that RbInBr3 and RbInCl3 possess promising potential for renewable energy applications.

Effect of bending deformation on the electronic and optical properties of O atoms adsorbed by Be3N2.

In this paper, the optimum coverage of 4.44% and the optimum adsorption sites were determined for the Be3N2 adsorption system of O atoms at different coverages based on density functional theory. The electronic and optical properties of the model were investigated by applying bending deformation to the model at these coverage and adsorption sites. Adsorption of O atoms disrupts the geometrical symmetry of Be3N2, resulting in orbital rehybridization and lowering its band gap. Bending deformation causes the band gap of the adsorbed O atom structure of Be3N2 to first increase and then decrease, resulting in the modulation of its band gap. With increasing bending deformation, the adsorbed system is redshifts, and the degree of redshift increases with increasing bending deformation. All calculations in this paper were performed using the first-principles-based CASTEP module of Materials Studio (MS). The generalized gradient approximation (GGA) plane-wave pseudopotential method and the Perdew-Burke-Ernzerhof (PBE) Perdew et al. Phys Rev Lett 77:3865, 1996 generalized functional were used in the geometry optimization and calculation process to calculate the exchange-correlation potential between electrons. The effect of coverage on the electronic and optical properties of the Be3N2-adsorbed O atom system was investigated by adsorbing different numbers of O atoms on a monolayer of Be3N2. The Be3N2 protocell contains two N atoms and three Be atoms with a space community of P6/MMM (No.191). The original cell was expanded 3 times along the direction of the base vectors a and b in the Be3N2 plane to create a 3 × 3 × 1 monolayer Be3N2 supercell system. A vacuum layer of 15Å is set in the direction of the crystal plane of the vertical monolayer Be3N2 supercell to eliminate interactions between adjacent layers. In the overall energy convergence test of the Be3N2 supercell, the plane wave truncation energy was set to 500eV, and the energy difference between the calculations given in the literature Reyes-Serrato et al. J Phys Chem Solids 59:743-6, 1998 using 550eV was less than 0.01eV, verifying the reliability of the data at a truncation energy of 500eV. The Monkhorst-Pack special k-point sampling method Monkhorst et al. Phys Rev B 13:5188, 1976 was used in the structural calculations, and the grid was set to 3 × 3 × 1. The geometric optimization parameters are set as follows: the self-consistent field iteration convergence criterion is 2.0 × 10-6eV, and the iterative accuracy convergence value is not less than 1.0 × 10-5eV/atom for the total force of each atom and less than 0.03eV/Å for all atomic forces. In addition the high-symmetry k-point path is taken as Γ(0,0,0) → M(0,0.5,0) → K(- 1/3,2/3,0) → Γ(0,0,0) Chen et al, AIP Adv 8:105105, 2018.

Study of the Phase Transition and Physical Properties of AlAs, ScAs and AlxSc1-XAs Compounds by the FP-LMTO Method

Abstract In this present work, we will study the physical properties of a brand new semiconductor material. the structural stability and the electronic properties of Scandium Arsenide (ScAs) and Aluminum Arsenide (AlAs) semiconductors as well as their ternary alloys (AlxSc1-xAs, 0≤ x≤1) in both rocksalt RS (B1) and zincblende ZB (B3). Calculations on both structures are done the method (FPLMTO, Full Potential Linear Muffin Tin). In the framework of density functional theory (DFT). The exchange-correlation potential was calculated using both the Local Density Approximation and the Generalized Gradient Approximation. The structural parameters of AlxSc1-xAs alloys, such as the lattice constant, the bulk module and its derivative are calculated. The lattice parameter deviates slightly from the line of Vegard’s Law in B3 structure, while the deviation was more pronounced in B1 structure. The calculations showed a phase transition from the ZnS phase (B3) to the RS phase (B1) at pressures (7, 10.5, 14.0 and 23.0 Gpa in LDA and (10.0, 12.5, 10.0 and 25.0 GPa) in GGA for x = 0.25, 0.50, 0.75 and 1.00) respectively.The calculated electronic properties showed that in phase B1, there exists an energy band (X-X) with a direct gap at x = 0.00. On the other hand, in phase B3, there are two kinds of energy bands, of direct gap (Γ-Γ) for x = 0.25, 075 and 1.00, the second band is of indirect gap (Γ-X) for x = 0.50, suggesting the possibility to be used in the long wavelength optoelectronic applications. The deviation of The calculated band gap deviation from linear behavior was significant in both structures. The AlxSc1-xAs alloys were found to be semiconducting at x=0 in the B1 phase and at x=0.25, 0.50, 0.75 and 1 in the B3 phase. Concerning calculations of the optical properties of the ternary AlxSc1-xAs alloy at concentrations x= 0.25, 0.50 and 0.75 in the ZnS (B3) phase, and from our bibliographic research we are sure that no reference exists in the literature. Our work can therefore be used as a reference for future research. Our simulation results are in good agreement with those obtained theoretically and experimentally.

Review of electron emission and electrical breakdown in nanogaps

With the continual miniaturization of electronic devices, there is an urgent need to understand the electron emission and the mechanism of electrical breakdown at nanoscale. For a nanogap, the complete process of the electrical breakdown includes the nano-protrusion growth, electron emission and thermal runaway of the nano-protrusion, and plasma formation. This review summarizes recent theories, experiments, and advanced atomistic simulation related to this breakdown process. First, the electron emission mechanisms in nanogaps and their transitions between different mechanisms are emphatically discussed, such as the effects of image potential (of different electrode's configurations), anode screening, electron space-charge potential, and electron exchange-correlation potential. The corresponding experimental results on electron emission and electrical breakdown are discussed for fixed nanogaps on substrate and adjustable nanogaps, including space-charge effects, electrode deformation, and electrical breakdown characteristics. Advanced atomistic simulations about the nano-protrusion growth and the nanoelectrode or nano-protrusion thermal runaway under high electric field are discussed. Finally, we conclude and outline the key challenges for and perspectives on future theoretical, experimental, and atomistic simulation studies of nanoscale electrical breakdown processes.

Influence of shear strain on the electronic properties of monolayers MoS2, WS2, and MoS2/WS2 vdW heterostructure.

This study investigates the dynamic stability of monolayers MoS2, WS2, and MoS2/WS2 van der Waals heterostructures (vdWHs) and the influence of shear strain on their electronic properties. The computational results of the binding energy and phonon dispersion demonstrate the excellent dynamic stability of MoS2/WS2 vdWHs. The MoS2/WS2 vdWH, with a type-II band alignment and an indirect bandgap, reduces electron-hole recombination, enhancing the efficiency and performance of optoelectronic devices. Under shear strain, the bandgap size and type of monolayers MoS2, WS2, and MoS2/WS2 vdWHs were effectively modulated, along with the interlayer charge redistribution in the MoS2/WS2 vdWHs. This work reveals the tunability of the electronic properties of monolayers MoS2, WS2, and MoS2/WS2 vdWHs under shear strain, offering new possibilities and solutions for developing optoelectronic devices, sensors, and related fields. This work employed the CASTEP module within the Materials Studio software package for first-principles calculations. Ultrasoft pseudopotentials were employed during geometry optimizations to account for ion-electron interactions using the GGA-PBE functional for exchange-correlation potentials. The electronic configurations of the S, Mo, and W atoms were chosen as their typical arrangements: (3s2p4), (4s2p6d55s1), and (5s2p6d46s2), respectively. A vacuum layer of 20Å was added to avoid interactions between the atomic layers. A cutoff energy of 500eV was set for structural optimization and self-consistent calculations, with k-point grids of 6 × 6 × 1 and 9 × 9 × 1. During the structural optimization process, the energy convergence criterion was set to 1 × 10-5eV, and the thresholds for interatomic forces and stresses were set to 0.01eV/Å and 0.01 GPa, respectively. Grimmer's DFT-D2 correction accounted for the interlayer vdW interactions in the MoS2/WS2 vdWH, while the phonon dispersion was calculated using the linear response method.

Theoretical investigation of structural, electronic, elastic, and optical properties of rubidium-based perovskites RbSrX3 (X = Cl, Br) for optoelectronic device applications – A DFT study

The search for environment-friendly lead-free halide perovskites is an emerging research area due to their crucial application in the field of photovoltaics and optoelectronics. So, in this current work, the structural, electronic, elastic, thermal, and optical properties of rubidium-based cubic halide perovskites RbSrX3 (X = Cl, Br) are investigated by the full potential linearized augmented plane wave (FP-LAPW) method in the context of density functional theory (DFT). The Generalized Gradient Approximation (GGA) of Perdew-Burke-Ernzerhof (PBE) is implemented as the exchange-correlation potential. The structural stability of these compounds in the cubic phase is studied and the values of their formation energies and ionic filling fraction (IFF) have been assessed. The band structure and DOS plots reveal a wide indirect bandgap at zero pressure. The elastic constants of these compounds are evaluated, and from Blackman's and Every's diagrams, they are found to be elastically stable with a ductile and anisotropic nature. The optical parameters of these compounds imply that they show good response in the ultraviolet region. Thus, by experimentally synthesizing these compounds their potential application in the development of optoelectronic devices working in UV range can be assessed.

Theoretical studies on phase stability, electronic, optical, mechanical and thermal properties of chalcopyrite semiconductors HgXN2 (X=Si, Ge and sn): A comprehensive DFT analysis

In this study, the ground state physical properties of Hg-based chalcopyrite semiconductors, HgXN2 (X = Si, Ge and Sn), are investigated using the density functional theory (DFT), which is based on full potential linearized augmented plane wave (FP-LAPW) method. The structural, electronic, optical, mechanical and thermal properties of the body-centered tetragonal (BTC) phase, HgXN2 (X = Si, Ge and Sn), have been calculated using the modified Becke-Johnson exchange-correlation potential (TB-mBJ). The obtained lattice parameters and volume are in good agreement with the values reported earlier, indicating that the results are reliable and reproducible. The phase stability of the titled compounds is elaborately studied and it is confirmed that all are thermodynamically, dynamically and mechanically stable. The electronic band structure demonstrated a direct band gap of 1.70 eV, 0.99 eV, and 0.94 eV for the HgXN2 (X = Si, Ge and Sn) compounds, respectively. Both HgGeN2 and HgSnN2 compounds have a notably lighter carrier effective mass, resulting in higher carrier mobility and conductivity than HgSiN2. The order of the mechanical hardness is as follows: HgSiN2> HgGeN2> HgSnN2. The studied materials are also anisotropic in mechanically and optically. All the title compounds exhibit ductile behavior. The charge density contour plots indicates the dominant covalent nature of the bonds in HgXN2 (X = Si, Ge and Sn). All these compounds have a high absorption coefficient and low optical reflectivity in the visible light range. Due to the favorable band gap and high absorption coefficient, these compounds could be suitable for optoelectronic or photovoltaic device applications. Moreover, the thermal expansion coefficient, thermal conductivity, melting point and fracture toughness behavior have been calculated, which also showed promise for thermal barrier coating (TBC) applications.

Lead-free alternative cation (Ethylammonium) in organometallic perovskites for thermoelectric applications.

Hybrid halide perovskites are gaining prominence as a promising option in the advancement of photovoltaic devices. Ethylammonium-based hybrid halide perovskites have demonstrated impressive characteristics, such as a reduced band gap, enhanced stability, and non-toxic properties. In this study, we have explored the structural, electronic, optical, and thermoelectric characteristics of Ethylammonium tin chloride. We have found that Ethylammonium tin chloride (EASnCl3) is a direct wide band gap semiconductor. Additionally, we conducted calculations for various optical parameters, including the dielectric function, absorption coefficient, and refractive index, across a photon energy spectrum ranging from 0 to 7eV. The research highlights the exceptional qualities of EASnCl3, which exhibits a high absorption coefficient and an elevated Seeback coefficient, among other favorable attributes. These findings position it as a promising material for cost-effective photovoltaic device applications, addressing concerns related to environmental stability. Fundamental properties based on the full-potential linearized augmented plane wave (FP-LAPW) method, this computation was performed using the WIEN2k simulation code. We utilized the exchange-correlation potentials PBE-GGA and KTB-mBJ to compute the optimized structure, density of states, and band structure of the material. In order to calculate the thermoelectric properties of the material, the Boltztrap simulation tool has been used. There are several critical absorbance parameters, including the Seeback coefficient, figure of merit, power factor, electrical conductivity, and thermal conductivity, concerning their carrier concentration and chemical potential, that have been taken into consideration.

Employing neural density functionals to generate potential energy surfaces.

With the union of machine learning (ML) and quantum chemistry, amid the debate between machine-learned functionals and human-designed functionals in density functional theory (DFT), this paper aims to demonstrate the generation of potential energy surfaces using computations with machine-learned density functional approximation (ML-DFA). A recent research trend is the application of ML in quantum sciences in the design of density functionals such as DeepMind's Deep Learning model (DeepMind21, DM21). Though science reported the state-of-the-art performance of DM21, the opportunity to utilize DeepMind's pretrained DM21 neural networks in computations in quantum chemistry has not yet been tapped. So far in the literature, the Deep Learning density functionals (DM21) have not been applied to generate potential energy surfaces. While the superior accuracy of DM21 has been reported, there is still a scarcity of publications that apply DM21 in calculations in the field. In this context, for the first time in literature, neural density functionals inferring 2D potential energy surfaces (ML-DFA-PES) based on machine-learned DFA-based computational method is contributed in this paper. This paper reports the ML-DFA-generated PES for C4H8, H2O, H2, and H2+ by employing a pretrained DM21m TensorFlow model with cc-pVDZ basis set. In addition, we also analyze the long-range behavior of DM21 based PES to investigate the ability to describe a system at long ranges. Furthermore, we compare PES diagrams from DM21 with popular DFT functionals (b3lyp/ PW6B95) and CCSD(T). In this method, 2D potential energy surfaces are obtained using a method that relies upon the neural network's ability to accurately learn the mapping between 3D electron density and exchange-correlation potential. By inserting Deep Learning inference in DFT with a pretrained neural network, self-consistent field (SCF) energy at different geometries along the coordinates of interest is computed, and then, potential energy surfaces are plotted. In this method, first, the electron density is computed mathematically, and this computed 3D electron density is used as a ML feature vector to predict the exchange correlation potential as a ML inference computed by a forward pass of pre-trained DM21 TensorFlow computational graph, followed by the computation of self-consistent field energy at multiple geometries, and then, SCF energies at different bond lengths/angles are plotted as 2D PES. We implement this in a python source code using frameworks such as PySCF and DM21. This paper contributes this implementation in open source. The source code and DM21-DFA-based PES are contributed at https://sites.google.com/view/MLfunctionals-DeepMind-PES .

STRUCTURAL, ELECTRONIC, AND OPTICAL PROPERTIES INVESTIGATION OF ZnSe CUBIC SPHALERITE COMPOUNDS USING DENSITY FUNCTIONAL THEORY (DFT)

Theoretical investigation of the structural, elastic, electronic and optical properties of ZnSe using the plane-wave pseudo potential formalism method of density functional theory with local density approximation (LDA) and generalized gradient approximation (GGA) as exchange-correlation potentials (DFT). The optimal structure of the binary semiconductor ZnSe crystallized in the complex phase of sphalerite was determined by studying the energy as a function of the basic unit volume. The calculated equilibrium lattice constants, bulk moduli and volumes are in reasonable agreement with the available experimental results. The electronic and chemical bonding properties were investigated by calculating the band structure, density of states and Mulliken population. We found that for ZnSe, the band gap of LDA is 1.33 eV and that of GGA is 1.34 eV. In addition, optical properties (absorption coefficients) were calculated.

Predictive analysis of a new FeVTe alloy from first principles: An excellent choice for thermoelectric applications

To predict the thermoelectric (TE), magnetic, and electrical properties of the novel half-Heusler FeVTe as well as its dynamical, mechanical, and structural stability, this investigation makes use of the WIEN2K code and the FP-LAPW technique, which relies on density functional theory (DFT). The exchange-correlation potential in this analysis is handled using the GGA-PBE approximation. According to our predicted results, we can draw the conclusion that this compound exhibits stability in the ferromagnetic (FM) type I phase and reveals a total magnetic moment of unity. From the computed band structure, FeVTe unveils half-metallic (HM) behaviour, showing metallic features in the spin-up direction and a semiconductor character in the downspin direction with an indirect bandgap of 1.27 eV. The alloy complies with the Slater-Pauling law based on the predicted spin-polarized magnetic moments (MMs). Also, the results obtained for the elastic constants suggest that this material is ductile, anisotropic, and mechanically stable. Moreover, this compound demonstrates a remarkable figure of merit at room temperature and elevated temperatures, suggesting its potential as promising material for thermoelectric applications.