Inclusion Of Spin-orbit Coupling Research Articles

Ab Initio Calculation of UV-vis Absorption of Parent Mg, Fe, Co, Ni, Cu, and Zn Metalloporphyrins.

Relativistic restricted active space (RAS) second-order multireference perturbation theory (MRPT2) methods, incorporating spin-orbit (SO) coupling perturbatively via state interaction (SO-MRPT2/RASSCF), were used to reproduce the absorption spectra of parent metalloporphyrins containing the Mg2+, Zn2+, Co2+, Ni2+, Cu2+, or FeCl2+ ions in the 12,500-40,000 cm-1 region. Particular attention was paid to the interaction between the porphyrin ring and the metal 3d electrons in states of different multiplicities (we used metal 3d and double d-shell or 3d' orbitals). For this class of compounds, the N-electron valence state perturbation theory (NEVPT2) method is superior to the complete active space perturbation theory (CASPT2) and successfully reproduces the energies of all four characteristic transitions (Q, B, N, and L) of closed-shell metalloporphyrins. Inclusion of SO coupling was found to have very little effect on excitation energies and oscillator strengths. For FeCl2+ porphyrin, we treated ligand-to-metal charge-transfer (LMCT; π,d), metal ligand field (d,d), and metal-to-ligand charge-transfer (MLCT; d,π*) transitions within the same framework. The broad and intense spectral features associated with its B (Soret) band are attributed to multiconfigurational LMCT (d,π*) bands involving strong metal-ligand orbital mixing.

The Study of $${\text{Br}}_{{\text{2}}}^{ + }$$ with Equation-of-Motion Coupled-Cluster Methods Including Spin-Orbit Coupling

The Study of $${\text{Br}}_{{\text{2}}}^{ + }$$ with Equation-of-Motion Coupled-Cluster Methods Including Spin-Orbit Coupling

The electronic structures and optical properties induced by spin-orbit-coupling in LiPbPO4 compound

Phosphate materials are excellent candidates for nonlinear optical materials, thus necessitating a comprehensive and in-depth study of them. Here, inspired by the interesting phenomenon induced by the spin-orbit coupling (SOC) effect, we extend it to LiPbPO4 compounds using a first-principles approach to probe the influence of SOC on the electronic structure and optical properties of post-transition metal compounds. The results show that only the bottom of the conduction band shows an energy level splitting with the inclusion of SOC, which is analyzed to come from the SOC in the Pb 6p state since the SOC in the O 2p state is very weak. The splitting of the conduction band triggers the decrease of the band gap and the change of the optical properties. The performance analysis shows that both the refractive index and the second harmonic generation (SHG) coefficient are enhanced with the inclusion of SOC, however, the change in the birefringence is insignificant, and it is further found that the enhanced SHG coefficient values are closer to the experimental values. In conclusion, our study reveals the impact of SOC effect on the electronic structure and optical properties of LiPbPO4 compounds, contributing to a deeper understanding of the nonlinear optical in post-transition metal compounds.

Critical assessment of G0W0 calculations for 2D materials: the example of monolayer MoS2

Two-dimensional (2D) materials combine many fascinating properties that make them more interesting than their three-dimensional counterparts for a variety of applications. For example, 2D materials exhibit stronger electron-phonon and electron-hole interactions, and their energy gaps and effective carrier masses can be easily tuned. Surprisingly, published band gaps of several 2D materials obtained with the GW approach, the state-of-the-art in electronic-structure calculations, are quite scattered. The details of these calculations, such as the underlying geometry, the starting point, the inclusion of spin-orbit coupling, and the treatment of the Coulomb potential can critically determine how accurate the results are. Taking monolayer MoS2 as a representative material, we employ the linearized augmented planewave + local orbital method to systematically investigate how all these aspects affect the quality of G0W0 calculations, and also provide a summary of literature data. We conclude that the best overall agreement with experiments and coupled-cluster calculations is found for G0W0 results with HSE06 as a starting point including spin-orbit coupling, a truncated Coulomb potential, and an analytical treatment of the singularity at q = 0.

Metal-bonded perovskite lead hydride with phonon-mediated superconductivity exceeding 46 K under ambient pressure

In the search for high-temperature superconductivity in hydrides, a plethora of multi-hydrogen superconductors have been theoretically predicted, and some have been synthesized experimentally under ultrahigh pressures of several hundred GPa. However, the impracticality of these high-pressure methods has been a persistent issue. In response, we propose a new approach to achieve high-temperature superconductivity under ambient pressure by implanting hydrogen into lead to create a stable few-hydrogen binary perovskite, Pb4H. This approach diverges from the popular design methodology of multi-hydrogen covalent high critical temperature (Tc ) superconductors under ultrahigh pressure. By solving the anisotropic Migdal–Eliashberg equations, we demonstrate that perovskite Pb4H presents a phonon-mediated superconductivity exceeding 46 K with inclusion of spin–orbit coupling, which is six times higher than that of bulk Pb (7.22 K) and comparable to that of MgB2, the highest Tc achieved experimentally at ambient pressure under the Bardeen, Cooper, and Schrieffer framework. The high Tc can be attributed to the strong electron–phonon coupling strength of 2.45, which arises from hydrogen implantation in lead that induces several high-frequency optical phonon modes with a relatively large phonon linewidth resulting from H atom vibration. The metallic-bonding in perovskite Pb4H not only improves the structural stability but also guarantees better ductility than the widely investigated multi-hydrogen, iron-based and cuprate superconductors. These results suggest that there is potential for the exploration of new high-temperature superconductors under ambient pressure and may reignite interest in their experimental synthesis in the near future.

Two-dimensional antiferromagnetic nodal-line semimetal and spin Hall effect in MnC4

Nodal-line semimetals, characterized by Dirac-like crossings along one dimensional k-space lines, represent a unique class of topological materials. In this study, we investigate the intriguing properties of room-temperature antiferromagnetic MnC4 and its nodal-line features both with and without spin–orbit coupling (SOC). In the absence of SOC, we identify a doubly degenerate Dirac-nodal line, robustly protected by a combination of time-reversal, mirror, and partial-translation symmetries. Remarkably, this nodal line withstands various external perturbations, including isotropic and anisotropic strain, and torsional deformations, due to the ionic-like bonding between Mn atoms and C clusters. With the inclusion of SOC, we observe a distinctive quasi-Dirac-nodal line that emerges due to the interplay between antiferromagnetism and SOC-induced spin-rotation symmetry breaking. Finally, we observed a robust spin Hall conductivity that aligns with the energy range where the quasi-nodal line appears. This study presents a compelling example of a robust symmetry-protected Dirac-nodal line antiferromagnetic monolayer, which has potential for applications in next-generation spintronic devices.

Study of electronic and transport properties of some topological semimetals XPtBi(X=Gd,Nd,Y) compounds

We have reported the electronic and thermoelectric properties of rare-earth half-Heusler XPtBi(X = Gd,Nd,Y) topological semimetals(TSMs)compounds from the perspective of density functional theory. We have reported that the inclusion of spin orbit coupling (SOC) made more dense bands near fermi level which will be able to tune the electronic bands and well controlled twisting of the spin order which is mostly applicable to spintronic applications. Our results show that the band gap crossing is more near fermi level by the inclusion of SOC. We have reported that LSDA + U has strong effect on unfilled X-f states and hence shifts the bands towards Fermi level. We have found different topological states in these compounds in spin up and spin down states for GdPtBi, NdPtBi and YPtBi. We have further reported the transport properties of these TSMs with and without SOC in terms of figure of merit. Our results confirm that with the inclusion of SOCs in YPtBi power factor get enhanced appreciably for thermoelectric uses.

Size effects on polaron formation in lead chloride perovskite thin films

Lead halide perovskites (LHP) are of interest for light-emitting applications due to the tunability of their bandgap across the visible and near-infrared spectrum (IR) coupled with efficient photoluminescence quantum yields (PLQY). It is widely speculated that photoexcited electrons and holes spatially separate into large negative (electron) and positive (hole) polarons. Polarons are expected to be optically active. With the observed optoelectronic signatures expecting to show potential excited states within the polaronic potential well. From the polaron excited-state we predict that large polarons should be capable of spontaneous emission, photoluminescence, in the mid-IR to far-IR regime based on the concept of inverse occupations within the polaron potential well. Here we use density functional theory (DFT), including spin–orbit coupling interactions, for calculations on a two-dimensional Dion-Jacobson (DJ) lead chloride perovskite atomistic model of various sizes as a host material for either negative or positive polarons to examine the effects of size on polaron formation. This work provides computational evidence that polaron formation through selective charge injection does not show the same level of localisation for positive and negative polarons.

First-principles calculation of electron-phonon coupling in doped KTaO3.

Background: Motivated by the recent experimental discovery of strongly surface-plane-dependent superconductivity at surfaces of KTaO 3 single crystals, we calculate the electron-phonon coupling strength, λ, of doped KTaO 3 along the reciprocal-space high-symmetry directions. Methods:Using the Wannier-function approach implemented in the EPW package, we calculate λ across the experimentally covered doping range and compare its mode-resolved distribution along the [001], [110] and [111] reciprocal-space directions. Results: We find that the electron-phonon coupling is strongest in the optical modes around the Γ point, with some distribution to higher k values in the [001] direction. The electron-phonon coupling strength as a function of doping has a dome-like shape in all three directions and its integrated total is largest in the [001] direction and smallest in the [111] direction, in contrast to the experimentally measured trends in critical temperatures. Conclusions: This disagreement points to a non-BCS character of the superconductivity. Instead, the strong localization of λ in the soft optical modes around Γ suggests an importance of ferroelectric soft-mode fluctuations, which is supported by our findings that the mode-resolved λ values are strongly enhanced in polar structures. The inclusion of spin-orbit coupling has negligible influence on our calculated mode-resolved λ values.

A Comprehensive Study of Electronic, Optical, and Thermoelectric Characteristics of Cs2PbI2Br2 Inorganic Layered Ruddlesden-Popper Mixed Halide Perovskite through Systematic First-Principles Analysis.

In this research, we present a comprehensive study on the influence of layer-dependent structural, electronic, and optical properties in the two-dimensional (2D) Ruddlesden-Popper (RP) perovskite Cs2PbI2Br2. Employing first-principles computations within the density functional theory method, including spin orbit coupling contribution, we examine the impact of various factors on the material. Our results demonstrate that the predicted 2D-layered RP perovskite Cs2PbI2Br2 structures exhibit remarkable stability both structurally and energetically, making them promising candidates for experimental realization. Furthermore, we observe that the electronic band gap and optical absorption coefficients of Cs2PbI2Br2 strongly depend on the thickness variation of the layers. Interestingly, Cs2PbI2Br2 exhibits a notable absorption coefficient in the visible region. Using a combination of density functional theory and Boltzmann transport theory, the thermoelectric properties were forecasted. The calculation involved determining the Seebeck coefficient (S) and other associated thermoelectric characteristics, such as electronic and thermal conductivities, as they vary with the chemical potential at room temperature. These findings open up exciting opportunities for the application of this 2D RP perovskite in solar cells and thermoelectric devices, owing to its unique properties.

Transition probabilities of the AgS(A[formula omitted][formula omitted] X[formula omitted]) emission including spin–orbit coupling effects and evidence of a novel band system

A systematic spectroscopic work using multireference configuration interaction (MRCI) and coupled cluster (CC) calculations was performed in conjunction with large basis sets for AgS. As a result, a more accurate dissociation energy of 17,542 cm−1 is predicted for the X2Π using an analytical potential energy curve, including spin–orbit effects. The calculated energy separation Te(A)∼ 10,500 cm−1 suggests that the AgS(A2Σ+→ X2Π) band system is in near-IR. An unobserved 32Π→ X2Π band system is predicted with Einstein coefficient for spontaneous emission of the orders of 104–105 s−1 in the UV region (342 nm). The radiative lifetimes for the A2Σ+ are of the order of ∼100 microseconds. The AgS(A) state presents a possible predissociation channel caused by interactions with the quartet 14Σ− and 14Π states. The spin–orbit coupling effects are considered in this work by utilizing the Breit–Pauli operator. The present findings are good references for future spectroscopic research concerning heavy-element sulfides.

Ultrafast control of laser-induced spin-dynamics scenarios on two-dimensional Ni3@C63H54 magnetic system.

The concept of building logically functional networks employing spintronics or magnetic heterostructures is becoming more and more popular today. Incorporating logical segments into a circuit needs physical bonds between the magnetic molecules or clusters involved. In this framework, we systematically study ultrafast laser-induced spin-manipulation scenarios on a closed system of three carbon chains to which three Ni atoms are attached. After the inclusion of spin-orbit coupling and an external magnetic field, different ultrafast spin dynamics scenarios involving spin-flip and long-distance spin-transfer processes are achieved by various appropriately well-tailored time-resolved laser pulses within subpicosecond timescales. We additionally study the various effects of an external magnetic field on spin-flip and spin-transfer processes. Moreover, we obtain spin-dynamics processes induced by a double laser pulse, rather than a single one. We suggest enhancing the spatial addressability of spin-flip and spin-transfer processes. The findings presented in this article will improve our knowledge of the magnetic properties of carbon-based magnetic molecular structures. They also support the relevant experimental realization of spin dynamics and their potential applications in future molecular spintronics devices.

The Influence of Spin‐Orbit Interaction on the Electron‐Phonon Coupling in Tl‐Rich Cubic AuCu3‐Type Superconductors: Comparison with La3Tl

AbstractIn this work, the role of spin‐orbit coupling (SOC) in ATl3 (A = Ca, Y, La, and Th) and La3Tl is investigated by theoretical investigation of their structural, electronic, elastic, mechanical, phonon, and electron–phonon interaction properties. The effect of SOC on the electronic band structures of these compounds is that some of the degeneracies at the high symmetry points that would exist in a scalar relativistic calculation without SOC are removed by considering this coupling. The replacement of La and Tl atoms in LaTl3 increases the value of the density of states at the Fermi level N() by a factor of 2.1. Furthermore, this replacement makes almost all phonon modes in La3Tl softer than those in LaTl3. Both softer phonon modes and higher N() make the electron–phonon interaction in La3Tl much stronger than in LaTl3. The presence of SOC increases the values of LaTl3 by 34% (from 1.151 to 1.542 K) and of ThTl3 by 65% (from 0.479 to 0.793 K), resulting in good agreement with the corresponding experimental values of 1.63 and 0.87 K. The inclusion of SOC also improves the agreement with the experiment for values of CaTl3, YTl3, and La3Tl.

CaPdBi: A Nontrivial Topological Candidate

In the framework of density functional theory, a comprehensive investigation of the mechanical, dynamical, and electronic properties of the compounds CaPdX (X= Sb and Bi) is performed. The investigated systems are both mechanically and dynamically stable. These compounds are claimed to be metallic by the electronic structure properties, with intriguing crossing points in the close proximity of the Fermi level. With spin orbit coupling (SOC) included, a gap appears at particular crossing points. The predicted electronic band structure shows that the d-states of Ca and Pd and the p-states of Bi and Sb dominate at the crossing sites. Inversion and time-reversal symmetry, together with the inclusion of SOC, demonstrate that CaPdBi is a Dirac metal. The calculated Z2 invariants for CaPdSb and CaPdBi are 0 and 1, which infer the trivial and non-trivial strong topological nature, respectively. As a whole, the investigated compound has future scope for its fascinating topological features, one amongst which is the presence of low-energy excitons (Dirac points).

Anisotropy in colossal piezoelectricity, giant Rashba effect and ultrahigh carrier mobility in Janus structures of quintuple Bi2X3 (X = S, Se) monolayers

Due to the asymmetric structures, two-dimensional Janus materials have gained significant attention in research for their intriguing piezoelectric and spintronic properties. In the present work, quintuple Bi2X3 (X = S, Se) monolayers (MLs) have been modified to create stable Janus Bi2X2Y (X ≠ Y = S, Se) MLs that display piezoelectricity in both the planes along with Rashba effect. The out-of-plane piezoelectric constant (d 33) is 41.18 (−173.14) pm V−1, while the in-plane piezoelectric constant (d 22) is 5.23 (6.21) pm V−1 for Janus Bi2S2Se (Bi2Se2S) ML. Including spin–orbit coupling in the Janus MLs results in anisotropic giant Rashba spin splitting (RSS) at the Γ point in the valence band, with RSS proportional to d 33. The Rashba constant along the Γ–K path, , is 3.30 (2.27) eV Å, whereas along Γ–M, is 3.58 (3.60) eV Å for Janus Bi2S2Se (Bi2Se2S) ML. The MLs exhibit ultrahigh electron mobility (∼5442 cm2V−1s−1) and have electron to hole mobility ratio of more than 2 due to their tiny electron-effective masses. The flexibility of the MLs allows for a signification alteration in its properties, like band gap, piezoelectric coefficient, and Rashba constant, via mechanical (biaxial) strain. For the MLs, band gap and d 33 value are enhanced with compressive strain. The d33 value of Janus Bi2Se2S reaches 4886.51 pm V−1 under compressive strain. The coexistence of anisotropic colossal out-of-plane piezoelectricity, giant RSS, and ultrahigh carrier mobilities in Janus Bi2S2Se and Bi2Se2S MLs showcase their tremendous prospects in nanoelectronic, piezotronics, and spintronics devices.

Type II multiferroic order in two-dimensional transition metal halides from first principles spin-spiral calculations

We present a computational search for spin spiral ground states in two-dimensional transition metal halides that are experimentally known as van der Waals bonded bulk materials. Such spin spirals break the rotational symmetry of the lattice and lead to polar ground states where the axis of polarization is strongly coupled to the magnetic order (type II multiferroics). We apply the generalized Bloch theorem in conjunction with non-collinear density functional theory calculations to find the spiralling vector that minimizes the energy and then include spin–orbit coupling to calculate the preferred orientation of the spin plane with respect to the spiral vector. We find a wide variety of magnetic orders ranging from ferromagnetic, stripy anti-ferromagnetic, 120∘ non-collinear structures and incommensurate spin spirals. The latter two introduce polar axes and are found in the majority of materials considered here. The spontaneous polarization is calculated for the incommensurate spin spirals by performing full supercell relaxation including spinorbit coupling and the induced polarization is shown to be strongly dependent on the orientation of the spiral planes. We also test the effect of Hubbard corrections on the results and find that for most materials LDA + U results agree qualitatively with LDA. An exception is the Mn halides, which are found to exhibit incommensurate spin spiral ground states if Hubbard corrections are included whereas bare LDA yields a 120∘ non-collinear ground state.

Heat reflux sonochemical synthesis of Cu3BiS3 quantum dots: Experimental and first-principles investigation of spin–orbit coupling on structural, electronic, and optical properties

Semiconductor quantum dots (QD) exhibit promising electrical and optical properties in photovoltaic cells by improving their stability and efficiency enhancement. Therefore, in this study, novel Cu3BiS3 (CBS) ultrafine QDs were synthesized to function as effective solar absorbers, using a facile heat reflux sonochemical synthesis process under inert (N2) atmosphere. Using high-resolution transmission electron microscopy (HRTEM) analysis, the size of CBS QDs was found to be in the range of 3–8 nm. Furthermore, the crystallite size (D), strain (ε), and dislocation density (δ) of the QDs were investigated in detail by confirming the orthorhombic wittichenite structure. The photocurrent density (PCD) of CBS QDs obtained at a voltage range of 0.5–1 V was found between 0.2 and 0.6 mA/cm2 under illumination; otherwise, it has a linear nature and good ohmic behavior in the range of − 0.1 V to + 0.1 V. In additionally, the spin–orbit coupling (SOC) interaction was computed using the Perdew–Burke–Ernzerhof (PBE) and Tran-Blaha-modified Becke–Johnson (TB-mBJ) functionals in the density functional theory (DFT) framework. The results showed a bandgap transition from direct to indirect with the inclusion of SOC, as confirmed by the electronic band structure. Moreover, the DFT-calculated bandgap using the TB-mBJ functional (∼1 eV) achieved near consistency with the experimentally obtained bandgap (∼1.4 eV). Therefore, based on the experimental and computational results, this study can pave the way toward developing novel copper chalcogenide QDs for application in future photovoltaic cells.

High-Temperature Thermodynamics of Uranium from Ab Initio Modeling

We present high-temperature thermodynamic properties for uranium in its γ phase (γ-U) from first-principles, relativistic, and anharmonic theory. The results are compared to CALPHAD modeling. The ab initio electronic structure is obtained from density-functional theory (DFT) that includes spin–orbit coupling and an added self-consistent orbital-polarization (OP) mechanism for more accurate treatment of magnetism. The first-principles method is coupled to a lattice dynamics scheme that is used to model anharmonic lattice vibrations, namely, Self-Consistent Ab Initio Lattice Dynamics (SCAILD). The methodology can be summarized in the acronym DFT + OP + SCAILD. Upon thermal expansion, γ-U develops non-negligible magnetic moments that are included for the first time in thermodynamic theory. The all-electron DFT approach is shown to model γ-U better than the commonly used pseudopotential method. In addition to CALPHAD, DFT + OP + SCAILD thermodynamic properties are compared with other ab initio and semiempirical modeling and experiments. Our first-principles approach produces Gibbs free energy that is essentially identical to CALPHAD. The DFT + OP + SCAILD heat capacity is close to CALPHAD and most experimental data and is predicted to have a significant thermal dependence due to the electronic contribution.

The effect of the spin–orbit coupling on the physical properties of ScGa[formula omitted] and LuGa[formula omitted] superconductors

In this work, we have aimed to reveal the impacts of spin–orbit coupling (SOC) on the elastic, mechanical, electronic, phonon, and electron–phonon interaction properties of ScGa3 and LuGa3 by executing both scalar and full-relativistic ab initio pseudopotential calculations based on the density functional theory with its local density approximation. The effect of this coupling on the physical properties of LuGa3 is slightly more pronounced than those of ScGa3. This finding has a physical explanation because spin–orbit interaction in an atom is due to the interaction of electronic spin moment with the magnetic field formed by the traveling electron in the electric field of the nucleus. Since the nuclear charge enhances with the rise in atomic number of the elements, heavier atoms are characterized by larger SOC strength and the mass of Lu atom is considerably heavier than that of Sc atom. In particular, the inclusion of SOC changes the value of the electron–phonon coupling parameter for LuGa3 from 0.593 to 0.583 by less 2%, while the corresponding parameter of ScGa3 remains almost unchanged (from 0.536 to 0.537). The superconducting transition temperature is estimated to be 2.09 K for ScGa3, and 2.15 K for LuGa3 are almost equal to their experimental values of 2.1 and 2.2 K, respectively. Finally, we have estimated three superconducting parameters: the Ginzburg–Landau parameter (κ(0)), the London penetration depth (λL(0)) and the coherence length (ξ(0)). Their calculated values confirm the existence of type-I superconductivity in both superconductors.

Structural, electronic, and optical properties of orthorhombic and hexagonal phases of Bi2Se3: First-principles study

In this work, we present structural, electronic, and optical properties of Bi2Se3 using first-principles calculations based on density functional theory (DFT) including spin orbit coupling (SOC)). Bi2Se3 is well known V–VIth group chalcogenide material shows excellent thermoelectric properties and suitable for optoelectronic devices. The calculations were performed using computational code SIESTA using generalized gradient approximation (GGA) Perdew–Burke–Eruzerhof for solids (PBESol) functionals. The obtained indirect band gaps of Bi2Se3 were 0.12 eV and 1.14 eV and obtained refractive index along x-direction were 5.48 and 1.96 for hexagonal and orthorhombic phases, respectively. The absorption results showed that the hexagonal Bi2Se3 absorb IR radiations while orthorhombic Bi2Se3 absorbs Nr-IR radiations. Hence both the phases of Bi2Se3 are suitable for detector applications. Bi2Se3 with large indirect band gap in orthorhombic phase is more suitable for band-to-band tunnelling transistors and optoelectronic devices.