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Register a new userFirst-Principles Understanding of the Electronic Band Structure of Copper-Antimony Halide Perovskite: The Effect of Magnetic Ordering
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We report the understanding of the electronic band structure of $Cs_4CuSb_2Cl_{12}$ perovskite through first-principles density-functional theory calculations. We find that the most stable state has the antiferromagnetic configuration where each $[CuCl_6]$ octahedral chain along the [010] direction is antiferromagnetic. The reasonable band structure of the compound can be obtained only if both the correct magnetic order and the improved exchange interaction of the Cu $it{d}$ electrons are taken into account.
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The molybdate oxides SrMoO$_3$, PbMoO$_3$, and LaMoO$_3$ are a class of metallic perovskites that exhibit interesting properties including high mobility, and unusual resistivity behavior. We use first-principles methods based on density functional theory to explore the electronic, crystal, and magnetic structure of these materials. In order to account for the electron correlations in the partially-filled Mo $4d$ shell, a local Hubbard $U$ interaction is included. The value of $U$ is estimated via the constrained random-phase approximation approach, and the dependence of the results on the choice of $U$ are explored. For all materials, GGA+$U$ predicts a metal with an orthorhombic, antiferromagnetic structure. For LaMoO$_3$, the $Pnma$ space group is the most stable, while for SrMoO$_3$ and PbMoO$_3$, the $Imma$ and $Pnma$ structures are close in energy. The $R_4^+$ octahedral rotations for SrMoO$_3$ and PbMoO$_3$ are found to be overestimated compared to the experimental low-temperature structure.
We performed a first-principles study of the structural, vibrational, electronic and magnetic properties of NaMnF3 under applied isotropic pressure. We found that NaMnF3 undergoes a reconstructive phase transition at 8 GPa from the Pnma distorted perovskite structure toward the Cmcm post-perovskite structure. This is confirmed by a sudden change of the Mn-F-Mn bondings where the crystal goes from corner shared octahedra in the Pnma phase to edge shared octahedra in the Cmcm phase. The magnetic ordering also changes from a G-type antiferromagnetic ordering in the Pnma phase to a C-type antiferromagnetic ordering in the Cmcm phase. Interestingly, we found that the high-spin d-orbital filling is kept at the phase transition which has never been observed in the known magnetic post-perovskite structures. We also found a highly non-collinear magnetic ordering in the Cmcm post-perovskite phase that drives a large ferromagnetic canting of the spins. We discuss the validity of these results with respect to the U and J parameter of the GGA+U exchange correlation functional used in our study and conclude that large spin canting is a promising property of the post-perovskite fluoride compounds.
Recent experiments reported giant magnetoresistance at room temperature in LaOMnAs. Here a density functional theory calculation is performed to investigate magnetic properties of LaOMnAs. The ground state is found to be the G-type antiferromagnetic order within the $ab$ plane but coupled ferromagnetically between planes, in agreement with recent neutron investigations. The electronic band structures suggest an insulating state which is driven by the particular G-type magnetic order, while a metallic state accompanies the ferromagnetic order. This relation between magnetism and conductance may be helpful to qualitatively understand the giant magnetoresistance effects.
We propose a design scheme for potential electrides derived from conventional materials. Starting with rare-earth-based ternary halides, we exclude halogens and perform global structure optimization to obtain thermodynamically stable or metastable phases but having an excess of electrons confined inside interstitial cavities. Then, spin-polarized interstitial states are induced by chemical substitution with magnetic lanthanides. To demonstrate the capability of our approach, we test with 11 ternary halides and successfully predict 30 stable and metastable phases of nonmagnetic electrides subject to 3 different stoichiometric categories, and successively 28 magnetic electrides via chemical substitution with Gd. 56 out of these 58 designed electrides are discovered for the first time. Two electride systems, the monoclinic $A$C ($A=$ La, Gd) and the orthorhombic $A_2$Ge ($A=$ Y, Gd), are thoroughly studied to exemplify the set of predicted crystals. Interestingly, both systems turn out to be topological nodal line electrides (TNLE) in the absence of spin-orbit coupling and manifest spin-polarized interstitial states in the case of $A=$ Gd. Our work establishes a novel computational approach of functional electrides design and highlights the magnetism and topological phases embedded in electrides.
The full-potential linearized augmented plane wave method with the generalized gradient approximation for the exchange-correlation potential (FLAPW-GGA) is used to predict the electronic and elastic properties of the newly discovered superconducting nanolaminate Ti2InC. The band structure, density of states and Fermi surface features are discussed. The optimized lattice parameters, independent elastic constants, bulk and shear moduli, compressibility are evaluated and discussed. The elastic parameters of the polycrystalline Ti2InC ceramics are estimated numerically for the first time.
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