Influence Of Spin-orbit Coupling Research Articles

A Computational Study on Closed-Shell Molecular Hexafluorides MF6 (M=S, Se, Te, Po, Xe, Rn, Cr, Mo, W, U) - Molecular Structure, Anharmonic Frequency Calculations, and Prediction of the NdF6 Molecule.

Quantum chemical methods were used to study the molecular structure and anharmonic IR spectra of the experimentally known closed-shell molecular hexafluorides MF6 (M=S, Se, Te, Xe, Mo, W, U). First, the molecular structures and harmonic frequencies were investigated using Density Functional Theory (DFT) with all-electron basis sets and explicitly considering the influence of spin-orbit coupling. Second, anharmonic frequencies and IR intensities were calculated with the CCSD(T) coupled cluster method and compared, where available, with IR spectra recorded by us. These comparisons showed satisfactory results. The anharmonic IR spectra provide means for identifying experimentally too little studied or unknown MF6 molecules with M=Cr, Po, Rn. To the best of our knowledge, we predict the NdF6 molecule for the first time and show it to be a true local minimum on the potential energy surface. We used intrinsic bond orbital (IBO) analyses to characterize the bonding situation in comparison with the UF6 molecule.

Impact of spin–orbit coupling on physical properties and superconductivity in noncentrosymmetric superconductors Ru[formula omitted]B[formula omitted] and Re[formula omitted]B[formula omitted

We have made a first-principles investigation of the effect of spin–orbit coupling (SOC) the physical properties and superconductivity of noncentrosymmetric hexagonal superconductors T7B3 (T = Ru and Re). In general, the influence of SOC on the electronic, elastic and mechanical properties is slightly larger for Re7B3 due to larger nuclear charge of Re as compared to that of Ru since the strength of this coupling varies as Z4 (Z is atomic number). For both compounds, the transition metal-related phonon modes form more than 90% of the electron–phonon coupling parameter. SOC is slightly more effective on the Eliashberg spectral function of Re7B3 than that of Ru7B3, increasing the electron–phonon coupling parameter for the former by around 3.0% and decreasing it by less than 1.0% for the latter. As a consequence, SOC increases the superconducting transition temperature of Re7B3 from 2.20 to 2.51 K and decreases that of Ru7B3 4.34 to 3.79 K.

LaIr3Ga2: A Superconductor Based on a Kagome Lattice of Ir

New materials based on Kagome lattices, predicted to host exotic quantum physics because they can display flat electronic bands, Dirac cones and topologically nontrivial surface states, are strongly desired. Here we report the crystal structure and superconducting properties of LaIr3Ga2, a previously unreported material that is based on a Kagome lattice of the heavy atom Ir. LaIr3Ga2 is a type II superconductor with Tc ~ 5.2 K, mu0Hc1 (0) ~ 7.1 mT and mu0Hc2 (0) ~ 4.7 T. The normalized heat capacity jump at the superconducting transition, (deltaC/gammaTc), 1.41, is within error of the value expected for a weak coupling BCS superconductor (1.43). Strong electron-electron correlation is inferred from the superconducting coherence length. Calculations show that the influence of spin orbit coupling on the electronic structure is significant, that the 5d states of the Ir in the Kagome planes are dominant near the Fermi energy (EF), that a nearly flat band is calculated to occur at about 100 meV below EF, and that two Dirac points are close to EF. This material is of interest for investigating the coupling between topological physics and superconductivity in a system with significant spin orbit coupling.

The effect of spin-orbit coupling on molecular properties: Potential energy curve, transition dipole moment and laser cooling scheme of NH

The influence of spin-orbit coupling on the cooling of NH molecular laser is investigated based on the ab initio theory. The potential energy curves (PECs) and spectral constants for four Λ-S states (X3Σ-, a1Δ, b1Σ+ and A3Π) and eight Ω states (X3Σ0+,1-,a1Δ2, b1Σ0++ and A3Π0-,0+,1,2) of NH molecule are obtained by the multi-reference configuration interaction (MRCI) plus Davidson correction. The spectroscopic constants (Re, ωe, ωeχe, Be, De) are obtained by solving the one dimensional radial Schrödinger equation, and the results are almost the same as the previously reported data. In addition, the transition dipole moment, permanent dipole moment, Franck-Condon factors, and radiative lifetime of NH molecule are also acquired. Also, the effects of the intermediate state on the X3Σ0+-↔A3Π1, X3Σ1-↔A3Π0+ and X3Σ1-↔A3Π0- transitions are considered. The feasible laser cooling schemes using a single laser are formulated. In the proposed cooling scheme, there wavelengths for the X3Σ0+-↔A3Π1 are used, the main pump lasers are λ00 = 335.74 nm. The feasible transition is based on this. It is found that spin-orbit coupling has a significant effect on potential energy curves, permanent dipole moments, transition dipole moments and vibration energy levels.

Covalency of Trivalent Actinide Ions with Different Donor Ligands: Do Density Functional and Multiconfigurational Wavefunction Calculations Corroborate the Observed "Breaks"?

A comprehensive ab initio study of periodic actinide-ligand bonding trends for trivalent actinides is performed. Relativistic density functional theory (DFT) and complete active-space (CAS) self-consistent field wavefunction calculations are used to dissect the chemical bonding in the [AnCl6]3-, [An(CN)6]3-, [An(NCS)6]3-, [An(S2PMe2)3], [An(DPA)3]3-, and [An(HOPO)]- series of actinide (An = U-Es) complexes. Except for some differences for the early actinide complexes with DPA, bond orders and excess 5f-shell populations from donation bonding show qualitatively similar trends in 5f n active-space CAS vs DFT calculations. The influence of spin-orbit coupling on donation bonding is small for the tested systems. Along the actinide series, chemically soft vs chemically harder ligands exhibit clear differences in bonding trends. There are pronounced changes in the 5f populations when moving from Pu to Am or Cm, which correlate with previously noted "breaks" in chemical trends. Bonding involving 5f becomes very weak beyond Cm/Bk. We propose that Cm(III) is a borderline case among the trivalent actinides that can be meaningfully considered to be involved in ground-state 5f covalent bonding.

Reliable TDDFT Protocol Based on a Local Hybrid Functional for the Prediction of Vibronic Phosphorescence Spectra Applied to Tris(2,2'-bipyridine)-Metal Complexes.

An efficient computational protocol for the prediction of vibrationally resolved phosphorescence spectra is developed and validated for five tris(2,2'-bipyridine)-metal complexes ([M(bpy)3]n+, where M = Zn, Ru, Rh, Os, Ir). The outstanding feature of this protocol is the use of full linear-response time-dependent density functional theory (TDDFT) for the excited-state triplet calculation, i.e., the commonly seen strategies employing the Tamm-Dancoff approximation (TDA) or unrestricted density functional theory (DFT) calculations for the T1 state are not needed. This is achieved by the use of a local hybrid functional (LH12ct-SsirPW92) that features a real-space dependent admixture of exact exchange governed by a local mixing function. The excellent performance of this LH for triplet excitation energies known from previous studies transfers to a remarkable mean absolute error of 0.06 eV for the phosphorescence 0-0 energies investigated herein, while the popular B3PW91 functional gives an error of 0.27 eV in TDDFT and 0.09 eV in unrestricted DFT calculations, respectively. The advantages of the local hybrid are particularly apparent for excited states with a mixed-valence character. The influence of spin-orbit coupling was found to be significant for [Os(bpy)3]2+ red-shifting the 0-0 energy for phosphorescence by 0.17 eV, while the effect is negligible for the other complexes (<0.03 eV). The influence of the basis-set and integration-grid sizes is evaluated, and a computationally lighter protocol is validated that leads to drastic savings in computation time with negligible loss in accuracy.

Transition of spin gapless semiconductor to semiconductor and half-metal in ferromagnetic Ba2MnTeO6

A novel spin gapless semiconductor material Ba2MnTeO6 is found and reported by first-principles calculations. In this paper, we study the influence of spin orbit coupling, strain and Coulomb interaction on the properties of ferromagnetic Ba2MnTeO6 in order to test the stability of physical properties. It turns out that the spin orbit coupling has no significant effect on the electronic structures of the Ba2MnTeO6 at equilibrium state. Under the action of uniform compressive strain and tensile strain, Ba2MnTeO6 transforms from spin gapless semiconductor to semiconductor and half-metal respectively. At the same time, as the strain increases, the semiconductor band gap gradually widens, and the half-metallic gap gradually narrows. After considering Coulomb interaction, Ba2MnTeO6 will also be transformed into a semiconductor, and the semiconductor band gap will increase with the increasing of U values. Furthermore, the mechanical performance studies show that Ba2MnTeO6 is an anisotropic material with stable structure. As the first pure double perovskite type spin gapless semiconductor, the high spin polarization and accurately adjustable physical properties of ferromagnetic Ba2MnTeO6 indicate that it has broad application prospects in the fields of spintronics and optoelectronic materials and devices.

All-electron MRCI+Q study on excited states of the SbBr molecule including spin-orbit coupling

In this work, we performed spin-orbit coupling (SOC) included MRCI+Q calculation on electronic states of SbBr. The SOC effect is treated by using the state interaction method in combination with the Breit-Pauli operator. Molecular orbitals are constructed with all-electron aug-cc-pwCVQZ-DK basis sets. Without SOC, total 34 Λ-S states of SbBr are obtained. It is found that the lowest three Λ-S states X3Σ−, a1Δ, and b1Σ+ are characterized by a common electron configuration (π2). All of them possess an especially deep potential well. Predissociations of a1Δ and b1Σ+ are illuminated with the aid of SO matrix elements. Under the influence of SOC, total 74 Ω states arise from Λ-S states. The energy splitting of X3Σ− is calculated to be 868 cm−1, which well reproduces the measurement of 873 cm−1. Particularly, SOC effects significantly improve the excitation energy (Te) of b1Σ+. The deviation is decreased from 1378 cm−1 to 233 cm−1. In addition, the SOC effect has a great effect on transition properties of SbBr. This effect is responsible for the phosphorescence of transitions a1Δ-X3Σ− and b1Σ+-X3Σ−, and the corresponding transition mechanism is elucidated. Finally, radiative lifetimes of a1Δ and b1Σ+ are determined at a millisecond level.

Electron correlation effect versus spin–orbit coupling for tungsten and impurities

The electron correlation and spin–orbit coupling (SOC) effects are investigated for body-centered-cubic tungsten and intrinsic & irradiative impurities using first principles calculations based upon the density functional theory. It is found that the electron correlation between the localized 5d electrons and the SOC effect are significant in modifying the band structures and the formation energies of defects. For the latter one, the involving of electron correlation always makes the defects stabler than the Perdew–Burke–Ernzerhof results, while the SOC contributes diversely for different defects. Moreover, the migration barrier of single tungsten vacancy moving in ⟨111⟩ direction is explored, where the inclusion of electron correlations remarkably decreases the migration barrier, while the influence of SOC is almost negligible. This study can help to validate the previous studies on irradiative defects in tungsten and improve the further investigations.

Fermi surface topology and nontrivial Berry phase in the flat-band semimetal Pd3Pb

A study of the Fermi surface of the putative topological semimetal Pd$_3$Pb has been carried out using Shubnikov-de Haas (SdH) oscillations measured in fields of up to 60 T. Pd$_3$Pb has garnered attention in the community due to a peculiar Fermi surface that has been proposed theoretically by Ahn, Pickett, and Lee, [Phys. Rev. B 98, 035130 (2018)] to host a dispersion-less band along $X-\Gamma$ as well as multiple triply-degenerate band crossings that, under the influence of spin-orbit coupling, lead to ten four-fold degenerate Dirac points. Analysis of the SdH oscillation data verifies the calculated multi-sheet Fermi surface, revealing a $\Gamma$ centered spheroid that had not been resolved experimentally in prior studies. A comprehensive, angle-dependent analysis of the phase of the SdH oscillations convincingly demonstrates a non-trivial Berry phase for two bands along $\Gamma-R$, supporting the theoretical predictions, while simultaneously evidencing interference between extremal orbits that mimics a trivial Berry phase at intermediate angles.

Investigation of the structural and electronic properties of InP1-xSbx alloy for mid-infrared optoelectronic applications: A TB-mBJ DFT study

The structural and electronic properties of InP1−xSbx supercell structure at different percent of Sb incorporation have been studied under the Density Functional Theory formalism employing WIEN2K package. From the total energy calculations, the supercell lattice structures have been optimized. The structural properties have been calculated from the equation of state which suggests the supercell structures to be significantly stable with a higher degree of compressive flexibility (specifically, at lower percent of Sb incorporation). The contribution of the partial and total DOS (Density of States) of constituent elements to total DOS of the supercell structure has been investigated. The relativistic effects have been assimilated into the band structure calculation, along various high symmetry k directions for each supercell structure. The values obtained for band gap (both, direct and indirect), spin-orbit splitting energy and bowing coefficient have been observed to vary significantly as a function of Sb mole fraction. Moreover, a relationship has been established between band gap (both, direct and indirect) values and spin-orbit splitting energy with Sb mole fraction. The influence of SOC (spin-orbit coupling) effect on the parameters concerning electronic properties has also been analyzed. The effective mass values for conduction and valence sub-bands (heavy hole, light hole and spin orbit split-off hole) near the Brillouin zone has been calculated at different percent of Sb incorporation in InP1−xSbx supercell structure. The interpretation of these results obtained suggests InP1−xSbx material to be competent for mid-infrared optoelectronic applications.

Brightened spin-triplet exciton induced by spin-orbit couplings in semiconducting carbon nanotubes

Firstly, the multi-band semiconductor Bloch equations (MB-SBE) for the quantum optical properties are reformulated in momentum space to investigate the influence of spin-orbit couplings (SOCs) on the linear optical response of semiconducting carbon nanotubes (SCNTs). One remarkable feature in numerical results is that a new low-strength peak appears at the lower-excited energy position than the peak E11. Comparing the data with/without SOCs, obviously, this new lowest-excited peak originates from the brightened spin-triplet exciton E11T, which has higher binding energy than the spin-singlet exciton E11S. For eight SCNTs with small radius, further comparison shows that the appearance and strength of this new peak E11T is dependent on the chiral of SCNTs. For (n, 1) tubes belonging to the family ν = +1 the effect of SOCs on this new brightened peak E11T is stronger relative to other SCNTs having the approximative strength of SOCs.

Spin-orbit coupling is the key to unraveling intriguing features of the halogen bond involving astatine.

The effect of spin-orbit coupling (SOC) on the halogen bond involving astatine has been investigated using state-of-the-art two- and four-component relativistic calculations. Adducts between Cl-X (X = Cl, Br, I and At) and ammonia have been selected to establish a trend on going down the periodic table. The SOC influence has been explored not only on the geometric and energetic features that can be used to characterize the halogen bond strength but also on the three main contributions to it that are the charge transfer, the "σ-hole" (i.e. the localized region with a net positive electrostatic potential at the halogen site) and the "polar flattening" (which is related to the effective shape of the halogen site). A surprisingly large increase of the Cl-At dipole moment, due to the inclusion of SOC, has been worked out using four-component CCSD(T) reference calculations, indicating that this bond is significantly more ionic than one may predict. Due to the SOC effect, which induces a peculiar charge accumulation on the At side in the Cl-At dimer, a weakening of the astatine-mediated halogen bond occurs arising from the (i) reduced amount of charge transfer, (ii) decrease of the polar flattening and (iii) lowering of the short-range Coulomb potential. The analysis of the electronic structure of the Cl-At moiety allows for a rationalization of the SOC effects on all the considered features of the halogen bond, including an unprecedented unsymmetrical charge back-donation from Cl-At to ammonia.

Soliton oscillation driven by spin-orbit coupling in spinor condensates

We theoretically investigate the dynamics of polar bright soliton under the influence of spin-orbit coupling (SOC) in spin-1 three component Bose-Einstein condensate (BEC). Periodically oscillating dark-bright-dark solitons are found to be induced by the SOC with their multifrequency oscillations jointly determined by the interparticle nonlinear interaction and the SOC strength. Explicit formulas are provided to identify these frequencies, which are in good agreement with the numerical simulation results. A linear Zeeman interaction is further introduced to break the time-reversal symmetry and change the polarity of the spinor BECs, which results in the periodic transition of the system from polar state to ferromagnetic state.

Four-component relativistic calculations of electronic excitations in tris-(allyl)-iridium complex: Influence of spin-orbit coupling on the electronic structure and excitation spectrum

Large-scale four-component relativistic calculations have been carried out for excited states of the tris-(allyl)-iridium complex, Ir(C3H5)3, using the relativistic polarization propagator method. The main focus was on providing insight into the lowest excited states of the three different structural forms of the complex, C3, C3h, and C1, including prediction of the excitation spectra and elucidation of spin-orbit coupling (SOC) effects for these forms. To unravel SOC effects, results of spin-orbit (SO) calculations were contrasted to results of spin-free (SF) calculations. Both the SO and SF calculations predict the lowest excited states of all three forms are of Rydberg type. We identified several Rydberg series, characterized by different hole configurations, that constitute the low-energy parts of the SO and SF excitation spectra. The SO spectra, however, differ notably from the corresponding SF spectra, pointing out to the influence of SOC. The most pronounced differences are observed for the SO and SF spectra of the C3h form. Our analysis indicates that SOC in this form causes strong alterations of the frontier occupied orbitals, participating in the excitations. As a result, excited states belonging to the first two Rydberg series are characterized by different electronic structure (hole configurations) in the SO and SF cases. Besides the orbital alteration effect, two other SOC effects, zero-field splitting and singlet-triplet mixing were identified in the SO spectra of all three forms. These effects result in new lines in the SO spectra and notable redistribution of the spectral intensity.

Coupling of spin-orbit interaction with phonon anharmonicity leads to significant impact on thermoelectricity in SnSe

Understanding the phonon transport in thermoelectric materials and its coupling with the complex environments is critical for manipulating the lattice thermal conductivity and consequently creating a high heat-to-electricity conversion efficiency. Spin-orbit coupling, an elementary interaction usually neglected when calculating lattice thermal conductivity, is intuitively expected to affect only the harmonic phonon properties in the materials. We herein studied the phonon transport in SnSe, a thermoelectric material with record-high energy conversion efficiency, by first-principle calculation and the Boltzmann transport equation. Spin-orbit coupling is found to greatly enhance its lattice thermal conductivity (up to ∼60%). More surprisingly, this enhancement originates from the influence of spin-orbit coupling on the phonon anharmonicity instead of the harmonic phonon properties. Spin-orbit coupling reduces the delocalization of the resonant bonding network formed by the p-orbitals of Se atoms, strengthens the interlayer Sn-Se bonds and consequently weakens the phonon anharmonicity. This discovery should encourage the design of tunable spin-orbit systems for better manipulation of thermoelectricity as well as other phonon transport related material functions.

Ab initio investigation of spin orbit coupling effect on the physical properties of IrGe superconductor

We have aimed to explore the influence of spin orbit coupling (SOC) on the electronic, elastic, mechanical, lattice dynamical and electron-phonon interaction properties of the simple orthorhombic IrGe using first principles density functional calculations within the generalized gradient approximation. The effect of SOC on the above properties of IrGe is mainly associated with Ir atom which possesses a 5d orbital and much heavier mass than that of Ge atom. The calculated values of nine independent elastic constants satisfy all the stability criteria, indicating that IrGe is mechanically stable in its MnP-type crystal structure. Also, no imaginary phonon frequencies are found in the phonon dispersion curves, indicating the dynamical stability of IrGe in its orthorhombic structure. Inclusion of SOC leads to the hardening of some low-frequency phonon modes which influences the electron-phonon interaction. Furthermore, inclusion of SOC leads to a decrease in dominant peaks of the Eliashberg function, and thus decrease in the values of the electron-phonon scattering parameter λ as well as the superconducting transition temperature Tc. Using the calculated value of λ with SOC, the value of Tc is obtained to be 5.09 K which compares very well with the recent measured value of 5.17 K.

Spin orbit coupling induced band gap in gemanene modulated by external field

We investigate the electronic band structure of germanene crystal by using the sixteen band tight-binding calculation. We focus on the modulation of its band gap with spin–orbit coupling (SOC), perpendicular electric field and magnetic field. Our calculation shows that the SOC opens a tunable band gap in the Dirac-type electronic structures, and plays a crucial rule in the formation of the energy band gap. The influence of SOC on the gap in germanene is much larger than that in graphene, which makes germanene an ideal candidate to exhibit the quantum spin Hall effect at room temperature. We also find that the electronic structure and topological property of germanene can be tuned by the external field significantly. Thus the electronic structure of germanene can be controlled to produce metallic, semiconducting, or insulating properties by applying an appropriate external field. In addition, the key features of the band structure induced by the electrical field and magnetic field are quite different. For the electric field applied, two spin-up states produce a gap at K point, in contrast, two spin-down states do it at K′ points. While for the magnetic field present, the band gaps are formed by the spin-up states from the conduction band and spin-down state from the valance band at both the K and K′ points. This modulation behavior of the band gap by the external field paves a way to the realization of germanene based spintronic devices.

Calculation of contact densities and Mössbauer isomer shifts utilising the Dirac-exact two-component normalised elimination of the small component (2c-NESC) method

ABSTRACTUtilizing the analytic derivative formalism for the Mössbauer isomer shift in connection with the Dirac-exact two-component Normalized Elimination of the Small Component (2c-NESC) method a new approach to the analytic calculation of the contact densities at the nuclei has been developed and implemented in the general purpose NESC programme. The new approach is applied to the calculation of the contact densities as well as contact density differences in several iodine-, gold-, and mercury-containing molecules. Substantial differences between the contact densities obtained by the spin-free 1c-NESC method and the 2c-NESC method are found, which demonstrate the importance of spin-orbit coupling. However, the influence of spin-orbit coupling on the contact density differences between the sample and the reference nuclei is found to be modest. This result suggests that a low-cost determination of accurate contact densities at the nuclei can be achieved by combining the 1c-NESC densities obtained at the correlated wavefunction level of theory with the contact density differences obtained at the 2c-NESC/DFT level.

Influence of Spin-Orbit Coupling in Iron-Based Superconductors.

We report on the influence of spin-orbit coupling (SOC) in Fe-based superconductors via application of circularly polarized spin and angle-resolved photoemission spectroscopy. We combine this technique in representative members of both the Fe-pnictides (LiFeAs) and Fe-chalcogenides (FeSe) with tight-binding calculations to establish an ubiquitous modification of the electronic structure in these materials imbued by SOC. At low energy, the influence of SOC is found to be concentrated on the hole pockets, where the largest superconducting gaps are typically found. This effect varies substantively with the k_{z} dispersion, and in FeSe we find SOC to be comparable to the energy scale of orbital order. These results contest descriptions of superconductivity in these materials in terms of pure spin-singlet eigenstates, raising questions regarding the possible pairing mechanisms and role of SOC therein.