Based on the first-principles calculations, we have investigated the geometry, binding properties, density of states and band structures of the novel superconductor LaFe1-xCoxAsO and its parent compounds with the ZrCuSiAs structure. We demonstrate that La-O bond and TM-As (TM=Fe or Co) bond are both strongly covalent, while the LaO and TMAs layers have an almost ionic interaction through the Bader charge analysis. Partial substitution of iron with cobalt modify the Fermi level from a steep edge to a flat slope, which explains why in this system Co doping suppresses the spin density wave (SDW) transition.
The hexagonal phase SrPtAs (s.g. P6/mmm; #194) with a honeycomb lattice structure very recently was declared as a new low-temperature (TC ~ 4.2K) superconductor. Here by means of first-principles calculations the optimized structural parameters, electronic bands, Fermi surface, total and partial densities of states, inter-atomic bonding picture, independent elastic constants, bulk and shear moduli for SrPtAs were obtained for the first time and analyzed in comparison with the related layered superconductor SrPt2As2.
Very recently, as an important step in the development of layered Fe-free pnictide-oxide superconductors, the new phase BaTi2Bi2O was discovered which has the highest TC (about 4.6 K) among all related non-doped systems. In this Letter, we report for the first time the electronic bands, Fermi surface topology, total and partial densities of electronic states for BaTi2Bi2O obtained by means of the first-principles FLAPW-GGA calculations. The inter-atomic bonding picture is described as a high-anisotropic mixture of metallic, covalent, and ionic contributions. Besides, the structural and electro…
We investigate the structural, electronic, and magnetic properties of stoichiometric LiFeAs by using state-of-the-arts first-principles method. We find the magnetic ground-state by comparing the total energies among all the possible magnetic orders. Our calculated internal positions of Li and As are in good agreement with experiment. Our results show that stoichiometric LiFeAs has almost the same striped antiferromagnetic spin order as other FeAs-based parent compounds and tetragonal FeSe do, and the experimental fact that no magnetic phase transition has been observed at finite temperature is…
Very recently the new low-temperature (TC ~ 3K) superconductor (SC) SrPd2Ge2 has been reported. This compound is isostructural with curently intensively studied group of so-called "122" SC's (based on tetragonal AM2Pn2 phases, where A are Sr, Ba; M are d metals and Pn are pnictogens: As or P), but it is pnictogen-free. Here, by means of first-principle FLAPW-GGA calculations, we have studied the electronic structure of new SC SrPd2Ge2. The band structure, total and partial densities of states and Fermi surface topology for SrPd2Ge2 are evaluated and discussed in comparison with those of isostr…
We have examined theoretically the electronic band structure and Fermi surface of tetragonal low-temperature superconductor Bi2Pd. Our main results are that (i) the Pd 4d and Bi 6p states determine the main peculiarities of the multiple-sheets FS topology, thus for this material the complicated superconducting gap structure with different energy gaps on different FS sheets should be assumed; (ii) the effect of the spin-orbit coupling is of minor importance for the distributions of the near-Fermi electronic states; and (iii) this phase adopts 3D-like type owing to the directional bonds between …
To explore the electronic structure of the first aromatic superconductor, potassium-doped solid picene which has been recently discovered by Mitsuhashi et al with the transition temperatures $T_c=7 - 20$ K, we have obtained a first-principles electronic structure of solid picene as a first step toward the elucidation of the mechanism of the superconductivity. The undoped crystal is found to have four conduction bands, which are characterized in terms of the maximally localized Wannier orbitals. We have revealed how the band structure reflects the stacked arrangement of molecular orbitals for b…
Based on First-principles calculation, we have investigated electronic structure of a ZrCuSiAs structured superconductor LaNiPO. The density of states, band structures and Fermi surfaces have been given in detail. Our results indicate that the bonding of the La-O and Ni-P is strongly covalent whereas binding property between the LaO and NiP blocks is mostly ionic. It's also found that four bands are across the Fermi level and the corresponding Fermi surfaces all have a two-dimensional character. In addition, we also give the band decomposed charge density, which suggests that orbital component…
By the first-principles electronic structure calculations, we have studied electronic structures of FeSe monolayer and bilayer thin films on SrTiO$_3$ (001) with SrO-termination or TiO$_2$ termination. We find that both FeSe monolayer and bilayer on either termination behave like a slightly doped semiconductor and a collinear antiferromagnetic order on Fe ions. There is no substantial charge transfer between the FeSe layers and the substrate. FeSe is adhered to the SrTiO$_3$ surface by a dipole-dipole interaction. The Fermi surface is mainly the contribution of Fe-3d orbitals. A valence band c…
We use the state-of-the-arts density-functional-theory method to study various magnetic orders and their effects on the electronic structures of the FeSe. Our calculated results show that, for the spins of the single Fe layer, the striped antiferromagnetic orders with distortion are more favorable in total energy than the checkerboard antiferromagnetic orders with tetragonal symmetry, which is consistent with known experimental data, and the inter-layer magnetic interaction is very weak. We investigate the electronic structures and magnetic property of the distorted phases. We also present our…
First-principles FLAPW-GGA band structure calculations were employed to examine the structural, electronic properties and the chemical bonding picture for four ZrCuSiAs-like Th-based quaternary pnictide oxides ThCuPO, ThCuAsO, ThAgPO, and ThAgAsO. These compounds were found to be semimetals and may be viewed as "intermediate" systems between two main isostructural groups of superconducting and semiconducting 1111 phases. The Th 5f states participate actively in the formation of valence bands and the Th 5f states for ThMPnO phases are itinerant and partially occupied. We found also that the bon…
First-principles, density-functional-based electronic structure calculations are employed to study the changes in the electronic properties of ZnC_{y}Ni_{3} and MgC_{y}Ni_{3} using the Korringa-Kohn-Rostoker coherent-potential approximation method in the atomic sphere approximation (KKR-ASA CPA). As a function of decreasing C at%, we find a steady decrease in the lattice constant and bulk modulus in either alloys. However, the pressure derivative of the bulk modulus displays an opposite trend. Following the Debye model, which relates the pressure derivative of the bulk modulus with the average…
BaPd2As2 belongs to 122 pnictide group, famous for exhibiting superconductivity at high temperatures and other electronic correlations. Unlike the 122 iron arsenides, BaPd2As2 exhibits superconductivity at low temperature when realized in theThCr2Si2 type structure (I4/mmm). We have performed density functional theory (DFT) based calculations to investigate the structural, elastic, electronic, thermodynamic, and optical properties of BaPd2As2 in this study. The structural, elastic, and the band structure features are compared with the available experimental and theoretical results. Pressure an…
Based on first-principle FLAPW-GGA calculations, we have investigated structural and electronic properties of the recently synthesized tetragonal (space group P4/nmm) nickel-based pnictide oxide superconductors: 3.3K (Ni2P2)(Sr4Sc2O6) and 2.7K (Ni2As2)(Sr4Sc2O6). Optimized structural data, electronic bands, total and partial densities of states, and Fermi surface topology have been obtained and discussed in comparison with available experiments and with their Fe-based (Fe2P2)(Sr4Sc2O6) and (Fe2As2)(Sr4Sc2O6) analogs.
First-principles calculations were performed to investigate electronic and elastic properties of the newly discovered 7.5K superconductor: layered Nb2InC. As a result, electronic bands, total and site-projected l- decomposed DOS at the Fermi level, shape of the Fermi surface for Nb2InC were obtained for the first time. Besides, independent elastic constants, bulk modulus, compressibility, shear modulus, Young's modulus, Poisson's ratio together with the elastic anisotropy parameters and indicator of brittle/ductile behavior of Nb2InC were evaluated and analyzed in comparison with the available…
By means of first-principles calculations? we have probed the peculiarities of the elecrtonic band structure and Fermi surface for the recently discovered layered superconductor LaO0.5F0.5BiSi2 in comparison with the parent phase LaOBiO2. The electronic factors prpmoting the transition of LaOBiS2 upon fluorine doping to superconducting state: inter-layer charge transfer, the evolution of the Fermi surface, and the dependence of the near-Fermi densities of states on x for LaO1-xFxBiS2 are evaluated and discussed in comparison with the available experiments.
The effect of doping on electronic and other related properties of PbO-type FeSe1-xTex has been investigated theoretically using density functional method. The elastic properties for mono- and poly-crystalline FeSe1-xTex system are predicted for the first time and the results discussed. Analysis of doping dependent band characteristics in conjunction with previous studies reveal that favorable nesting of Fermi surface indicates a possible basis for understanding why Tc in FeSe1-xTex is maximum for x ~ 0.5. Keywords: FeSe superconductors, Substitution effect, Elastic properties, Electronic prop…
In order to assist the search of new superconductors in iron selenide materials by intercalation, we calculate the crystal and electronic structures of MgOFeSe using the first-principles density functional theory. MgOFeSe is isotructural to the parent compound of iron pnictide superconductor LaOFeAs. In LaOFeAs, the anion O$^{2-}$ is located at the center of each LaO tetrahedra. But for MgOFeSe, we find that the crystal structure with the cation Mg$^{2+}$ as the tetrahedral center in the MgO layer is energetically more stable. The low energy band structures around the Fermi surfaces of MgOFeSe…
The full-potential linear augmented plane-wave calculations have been applied to investigate the systematic change of electronic structures in CaAlSi due to different stacking sequences of AlSi layers. The present ab-initio calculations have revealed that the multistacking, buckling and 60 degrees rotation of AlSi layer affect the electronic band structure in this system. In particular, such a structural perturbation gives rise to the disconnected and cylindrical Fermi surface along the M-L lines of the hexagonal Brillouin zone. This means that multistacked CaAlSi with the buckling AlSi layers…
Electronic structures of three superconducting rare-earth iron silicides (Lu;Y;Sc)2Fe3Si5 and non-superconducting Lu2Ru3Si5, adopting a tetragonal crystal structure (P4/mnc), have been calculated employing the full-potential local-orbital method within the density functional theory. The investigations were focused particularly on the band structures and Fermi surfaces, existing in four bands and containing rather three-dimensional electronlike and holelike sheets. They support an idea of unconventional multi-band superconductivity in these ternaries, proposed earlier by other authors for Lu2Fe…
Using a 72-atom supercell we report ab initio calculations of the electronic and vibrational densities of states for the bismuth (111) bilayers (bismuthene) with periodic boundary conditions and a vacuum of 5 Å, 10 Å and 20 Å. We find that the electronic density of states shows a metallic character at the Fermi level and that the vibrational density of states manifests the expected gap due to the layers. Our results indicate that a vacuum down to 5 Å does not affect the electronic and vibrational structures noticeably. A comparison of present results with those obtained for the Wyckoff structu…
The superconductor UCoGe is analyzed with electronic structure calculations using Linearized Augmented Plane Wave method based on Density Functional Theory. Ferromagnetic and antiferromagnetic calculations with and without correlations (via LDA+U) were done. In this compound the Fermi level is situated in a region where the main contribution to DOS comes from the U-5f orbital. The magnetic moment is mainly due to the Co-3d orbital with a small contribution from the U-5f orbital. The possibility of fully non-collinear magnetism in this compound seems to be ruled out. These results are compared …
We report a first-principles Wannier function study of the electronic structure of PdTe. Its electronic structure is found to be a broad three-dimensional Fermi surface with highly reduced correlations effects. In addition, the higher filling of the Pd $d$-shell, its stronger covalency resulting from the closer energy of the Pd-$d$ and Te-$p$ shells, and the larger crystal field effects of the Pd ion due to its near octahedral coordination all serve to weaken significantly electronic correlations in the particle-hole (spin, charge, and orbital) channel. In comparison to the Fe Chalcogenide e.g…
Based on first-principles FLAPW-GGA calculation, we have investigated electronic structure of newly discovered oxygen-free 38K superconductor Ba1-xKxFe2As2 in comparison with parent phase - tetragonal ternary iron arsenide BaFe2As2. The density of states, magnetic properties, near-Fermi bands compositions, together with Sommerfeld coefficients and molar Pauli paramagnetic susceptibility are evaluated. The results allow us to classify these systems as quasi-two-dimensional ionic metals, where the conduction is strongly anisotropic, only happening on the (Fe-As) layers. According to our calculat…
Although correlated electronic-structure calculations explain very well the normal state of Sr$_2$RuO$_4$, its superconducting symmetry is still unknown. Here we construct the spin and charge fluctuation pairing interactions based on its correlated normal state. Correlations significantly reduce ferromagnetic in favor of antiferromagnetic fluctuations and increase inter-orbital pairing. From the normal-state Eliashberg equations, we find spin-singlet $d$-wave pairing close to magnetic instabilities. Away from these instabilities, where charge fluctuations increase, we find two time-reversal sy…
Based on first-principles FLAPW-GGA calculations, we have investigated the electronic structure of newly synthesized novel superconductors LaONiBi and LaOCuBi, the first bismuth-containing compounds from the family of quaternary oxypnictides which attract now a great deal of interest in search for novel 26-55K superconductors. The band structure, density of states and Fermi surfaces are discussed. Our results indicate that the bonding inside of the (La-O) and (Ni(Cu)-Bi) layers is covalent whereas the bonding between the (La-O) and (Ni(Cu)- Bi) blocks is mostly ionic. For both oxybismuthides, …
We present a theoretical study on the superconductivity of $β'$-(BEDT-TTF)$_2$ICl$_2$ at $T_{\rm c}=$14.2 K under a high hydrostatic pressure recently found, which is the highest among organic superconductors. In the present work, we study an effective model using the fluctuation-exchange (FLEX) approximation based on the results of first-principles calculation. In the obtained phase diagram, the superconductivity with $d_{xy}$-like symmetry is realized next to the antiferromagnetic phase, as a result of the one-dimensional to two-dimensional crossover driven by the pressure.
The electronic structure of quasi-one-dimensional superconductor K$_2$Cr$_3$As$_3$ is studied through systematic first-principles calculations. The ground state of K$_2$Cr$_3$As$_3$ is paramagnetic but very close to a ferromagnetic instability. Close to the Fermi level, the Cr-3d$_{z^2}$, d$_{xy}$, and d$_{x^2-y^2}$ orbitals dominate the electronic states, and three bands cross $E_F$ to form one 3D Fermi surface sheet and two quasi-1D sheets. The electron DOS at $E_F$ is less than 1/3 of the experimental value, indicating an intermediate electron renormalization factor around $E_F$. Despite of…
Using the structural data of the La2CuO4 compound both in the low temperature tetragonal phase and in the isotropic phase we have derived an effective t-J model with hoppings t and superexchange interactions J extended up to fourth and second neareast neighbors respectively. By numerically studying this hamiltonian we have then reproduced the main experimental features of this HTc compound: d-wave superconductivity is stabilized at small but finite doping delta>6% away from the antiferromagnetic region and some evidence of dynamical stripes is found at commensurate filling 1/8.
We perform first-principles calculation to study the electronic structure of HgBa$_{2}$Ca$_{n-1}$Cu$_{n}$O$_{2n+2+x}$ copper oxides up to $n = 6$ for the undoped parent compound $(x = 0)$ and up to $n = 3$ for the doped compound $(x > 0)$ by means of the SCAN meta-GGA density functional. Our calculations predict an antiferromagnetic insulator ground state for the parent compounds with an energy gap that decreases with the number of CuO$_{2}$ planes. We report structural, electronic and magnetic order evolution with $x$ which agree with experiments. We find an enhanced density of states at Ferm…
