Pressure-induced reconstructive phase transitions, polarization with metallicity, and enhanced hardness in antiperovskite MgCNi.

In general, hydrostatic pressure can suppress electrical polarization, instead of creating and/or enhancing polarization like strain engineering. Here, a combination of first-principles calculations and CALYPSO crystal structures prediction is used to point out that hydrostatic pressure applied on antiperovskite MgCNi can stabilize polarization with metallicity, and thus a polar metal can exist under high pressure. Strikingly, the metallic polar phase of MgCNi exhibits an original linear-cubic coupling between polar and nonpolar modes, resulting in an asymmetrical double-well when the polarization is switched.

Strain-induced structural phase transition, electric polarization and unusual electric properties in photovoltaic materials CsMI (M = Pb, Sn).

The structural phase transition, ferroelectric polarization, and electric properties have been investigated for photovoltaic films CsMI (M = Pb, Sn) epitaxially grown along (001) direction based on the density functional theory. The calculated results indicate that the phase diagrams of two epitaxial CsPbI and CsSnI films are almost identical, except critical transition strains varying slightly. The epitaxial tensile strains induce two ferroelectric phases 2, and 2, while the compressive strains drive two paraelectric phases 222, 222.

Hydrostatic pressure induced structural phase transition and mechanical properties of fluoroperovskite.

We perform the first-principles calculations combined with the particle swarm optimization algorithm to investigate the high-pressure phase diagrams of Na[Formula: see text]F ([Formula: see text]  =  Mn, Ni, Zn). Two reconstructive phase transitions are predicted from Pv-[Formula: see text] to pPv-[Formula: see text] at about 9 GPa and pPv-[Formula: see text] to ppPv-[Formula: see text] at around 26 GPa for NaZnF. That is not the case for NaMnF-a direct transition (reconstructive transition in nature but with the same Pnma space group) from Pv-[Formula: see text] to ppPv-[Formula: see text] phase around 12 GPa.

Large polarization and dielectric response in epitaxial SrZrO3 films.

First-principles calculations are performed to investigate the ferroelectric and dielectric properties of (001) epitaxial SrZrO3 thin films under misfit strain. A rich phase diagram is predicted. By condensing the polar instability, the ferroelectric Pmc21 and Ima2 phases can coexist under tensile strain (about 3.

Creating multiferroics with large tunable electrical polarization from paraelectric rare-earth orthoferrites.

The quest for materials possessing both a magnetic ordering temperature above room temperature and a large electrical polarization is an important research direction in order to design novel spintronic and memory devices. Up to now, BiFeO3 and related systems are the only known compounds simultaneously possessing such characteristics. Here, first-principles calculations predict that another family of materials, namely epitaxial films made of rare-earth orthoferrites (RFeO3), can also exhibit such desired features.

Studies of EPR spectra and defect structure for Er³⁺ ions in BaF₂ and SrF₂ crystals.

The local lattice structure and electron paramagnetic resonance (EPR) spectra have been studied systematically by diagonalizing 364 × 364 complete energy matrices for a f(11) ion in a trigonal ligand-field. By simulating the calculated Stark levels and EPR parameters to the experimental results, the shift parameters are determined for Er(3+) ions in BaF(2) and SrF(2). The results show that the trigonal center is attributed to an interstitial F(-) ion located at the [111] axis of the cube, and the nearest ligand close to the charge compensator has a displacement towards central ion by 0.

Density functional study on size-dependent structures, stabilities, electronic and magnetic properties of Au(n)M (M = Al and Si, n = 1-9) clusters: comparison with pure gold clusters.

The density functional theory (DFT) method has been employed to systematically investigate the geometrical structures, relative stabilities, and electronic and magnetic properties of Au(n)M (M = Al and Si, n = 1-9) clusters for clarifying the effect of Al(Si) modulation on the gold nanostructures. Of all the clusters studied, the most stable configurations adopt a three-dimensional structure for Au(n)Al at n = 4-8 and Au(n)Si at n = 3-9, while for pure gold systems, no three-dimensional lowest energy structures are obtained. Through a careful analysis of the fragmentation energy, second-order difference of energy, HOMO-LUMO energy gap, and magnetic moment as a function of cluster size, an odd-even alternative phenomenon has been observed.

Determination of structures, stabilities, and electronic properties for bimetallic cesium-doped gold clusters: a density functional theory study.

The equilibrium geometric structures, stabilities, and electronic properties of bimetallic Au(n)Cs (n = 1-10) and pure gold Au(n) (n ≤ 11) clusters have been systematically investigated by using density functional theory with meta-generalized gradient approximation. The optimized geometries show that one Au atom capped on Au(n-1)Cs structures and Cs atom capped Au(n) structures for different sized Au(n)Cs (n = 1-10) clusters are two dominant growth patterns. Theoretical calculated results indicate that the most stable isomers have three-dimensional structures at n = 4 and 6-10.

A DFT study on equilibrium geometries, stabilities, and electronic properties of small bimetallic Na-doped Au(n) (n = 1-9) clusters: comparison with pure gold clusters.

A systematic study on the geometric structures, relative stabilities, and electronic properties of small bimetallic Au(n)Na (n = 1-9) clusters has been performed by means of first-principle density functional theory calculations at the PW91PW91 level. The results show that the optimized ground-state isomers adopt planar structures up to n = 5, and the Na-capped geometries are dominant growth patterns for n = 6-9. Dramatic odd-even alternative behaviors are obtained in the second-order difference of energies, fragmentation energies, highest occupied-lowest unoccupied molecular orbital energy gaps, and chemical hardness for both Au(n)Na and Au(n+1) clusters.

Theoretical study on local defect structure of (FeO4)(5-) clusters in YGG and LGG crystals.

The optical spectrum and the local defect structure of tetrahedral (FeO4)(5-) clusters are investigated in yttrium gallium garnet (YGG) and lutetium gallium garnet (LGG) crystals by means of the 252x252 complete energy matrices for d(5) configuration ions in tetragonal ligand field. The results show that the local defect structures around tetrahedral Fe3+ centers display an expansion effect. Simultaneously, the (FeO4(5-) clusters in the two different crystals have very similar local structures, which are close to those in YIG garnet crystal.

Tetragonal distortion of structural defects in Cr3+ doped in several perovskites calculated from the EPR and optical data: a complete energy matrix study.

This paper describes a novel application of a ligand field model in the study of the local molecular structure of the (CrF 6) (3-) coordination complex. Based on the ligand field model, the complete energy matrix which contains the electron-electron repulsion interaction, the ligand field interaction, the spin-orbit coupling interaction, and the Zeeman interaction, has been constructed for a d (3) configuration ion in a tetragonal ligand field. In order to study the relation between the EPR, the optical spectra, and the local lattice structures around the centers with tetragonal symmetry in AMF 3 codoped with Cr (3+) and Li (+) ions, a three-layer-ligand model is proposed.

Theoretical study of EPR spectra for Mn2+ ion in [Mg(H2O)6]SnCl6 single crystal.

The relationship between the impurity structures and the electron paramagnetic resonance (EPR) parameters D, (a-F) have been studied by diagonalizing the complete energy matrices for Mn2+ ion in [Mg(H2O)6]SnCl6 single crystal in a trigonal ligand field within a weak-field-representation. It is shown that the local lattice structure around Mn2+ ion in [Mg(H2O)6]SnCl6 exhibits an elongation distortion which is different at 290 K and 77 K. The local structure parameters R=2.

EPR theoretical study of local molecular structure and thermal expansion coefficient for octahedral Mn2+ centers in zinc fluosilicate.

A theoretical method for studying the inter-relation between electronic and molecular structure has been proposed by diagonalizing the complete energy matrices for a d(5) configuration ion in a trigonal ligand field and considering the second-order and fourth-order EPR parameters D and (a - F) simultaneously. As for ZnSiF(6).6H(2)O:Mn(2+) and ZnSiF(6).