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.

Probing the Structural and Electronic Properties of Dirhenium Halide Clusters: A Density Functional Theory Study.

Dirhenium halide dianions received considerable attention in past decades due to the unusual metal-metal quadruple bond. The systematic structural evolution of dirhenium halide clusters has not been sufficiently studied and hence is not well-understood. In this work, we report an in-depth investigation on the structures and electronic properties of doubly charged dirhenium halide clusters ReX (X = F, Cl, Br, I).

Structural Stability and Evolution of Medium-Sized Tantalum-Doped Boron Clusters: A Half-Sandwich-Structured TaB Cluster.

Transition-metal (TM)-doped boron clusters have received considerable attention in recent years, in part, because of their remarkable size-dependent structural and electronic properties. However, the structures of medium-sized boron clusters doped with TM atoms are still not well-known because of the much increased complexity of the potential surface as well as the rapid increase in the number of low-energy isomers, which are the challenges in cluster structural searches. Here, by means of an unbiased structure search, we systematically investigated the structural evolution of medium-sized tantalum-doped boron clusters, TaB (n = 10-20).

Exploration of the Structural, Electronic and Tunable Magnetic Properties of Cu₄M (M = Sc-Ni) Clusters.

The structural, electronic and magnetic properties of Cu₄M (M = Sc-Ni) clusters have been studied by using density functional theory, together with an unbiased CALYPSO structure searching method. Geometry optimizations indicate that M atoms in the ground state Cu₄M clusters favor the most highly coordinated position. The geometry of Cu₄M clusters is similar to that of the Cu₅ cluster.

Prediction of hypervalent molecules: investigation on MC (M = Li, Na, K, Rb and Cs; n = 1-8) clusters.

New hypervalent molecules have emerged from a systematic exploration of the structure and bonding of MC (M = Li, Na, K, Rb and Cs; n = 1-8) clusters via an unbiased CALYPSO structure investigation combined with density functional theory. The global minimum structures are obtained at the B3LYP/6-311+G* and CCSD(T)/6-311+G* levels of theory. The observed growth behavior clearly indicates that the ground state of MC (M = Li, Na, K, Rb and Cs; n = 1-8) is transformed from a planar to a three-dimensional (3D) structure at n = 4.

Evolution of the Structural and Electronic Properties of Medium-Sized Sodium Clusters: A Honeycomb-Like Na Cluster.

Sodium is one of the best examples of a free-electron-like metal and of a certain technological interest. However, an unambiguous determination of the structural evolution of sodium clusters is challenging. Here, we performed an unbiased structure search among neutral and anionic sodium clusters in the medium size range of 10-25 atoms, using the Crystal structure AnaLYsis by Particle Swarm Optimization (CALYPSO) method.

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.

Understanding the structural transformation, stability of medium-sized neutral and charged silicon clusters.

The structural and electronic properties for the global minimum structures of medium-sized neutral, anionic and cationic Sin(μ) (n = 20-30, μ = 0, -1 and +1) clusters have been studied using an unbiased CALYPSO structure searching method in conjunction with first-principles calculations. A large number of low-lying isomers are optimized at the B3PW91/6-311 + G* level of theory. Harmonic vibrational analysis has been performed to assure that the optimized geometries are stable.

Theoretical studies of the dependence of EPR parameters on local structure for the tetragonal Er(3+) centres in YVO4 and ScVO4.

The dependences of the EPR parameters on the local distortion parameters Δθ and ΔR as well as the crystal-field parameters have been studied by diagonalizing the 364×364 complete energy matrices for a tetragonal Er(3+) centre in the YVO4 and ScVO4 crystals. The results show that the local distortion angle Δθ and the fourth-order crystal-field parameter Ā4 are most sensitive to the EPR g-factors g// and g⊥, whereas the local distortion length ΔR and the second-order parameter Ā2 are less sensitive to the g-factors. Furthermore, we found that the abnormal EPR g-factors for the Er(3+) ion in the ScVO4 may be ascribed to the stronger nephelauxetic effect and covalent bonding effect, as a result of an expanded local distortion for the Er(3+) centre in the ScVO4 crystal.

Chemisorption-induced two- to three-dimensions structural transformations in gold pentamer (CO)(n)Au5(-) (n =0-5).

Understanding the geometry structures of gold clusters, especially with adsorbates, is essential for designing highly active gold nanocatalysts. Here, CO chemisorption onto the Au5(-) cluster is investigated using the density functional calculations. It is found that chemisorption of CO molecules can induce previously unreported two- to three-dimensions (3D) structural changes.

Probing the structural and electronic properties of small aluminum dideuteride clusters.

Adsorption of deuterium on the neutral and anionic Aln(λ) (n=1-9, 13; λ=0, -1) clusters has been investigated systematically using density functional theory. The comparisons between the Franck-Condon factor simulated spectra and the measured photoelectron spectroscopy (PES) of Cui and co-workers help to search for the ground-state structures. The results showed that D2 molecule tends to be dissociated on aluminum clusters and forms the radial AlD bond with one aluminum atom.

Probing the structural and electronic properties of bimetallic chromium-gold clusters CrmAun(m+n≤6): comparison with pure chromium and gold clusters.

Bimetallic chromium-gold CrmAun(m+n≤6) clusters are systematically investigated using the density functional theory at PW91P86 level with LanL2TZ basis set to understand the evolution of various structural, electronic, magnetic, and energetic properties as a function of size (m+n) and composition (m/n) of the system. Theoretical results show a logical evolution of the properties depending on the size and the composition of the system. Cr m clusters clearly prefer 3D structures while Au n clusters favor planar configurations.

Probing the geometries, relative stabilities, and electronic properties of neutral and anionic Ag(n)S(m) (n + m ≤ 7) clusters.

The geometry structures, relative stabilities, and electronic properties of neutral and anionic Ag(n)S(m) (n + m ≤ 7) clusters have been investigated systematically by means of density function theory (DFT). The results of geometry optimization show that the most stable configurations of binary Ag(n)S(m)⁰/⁻ clusters have an early appearance of 3D structure at n = 3, m = 1, differing from those of pure silver and sulfur clusters. Moreover, the ground-state structures prefer low spin multiplicity (singlet or doublet) except for S₂, Ag₂S₃, Ag₂S₄, Ag₄S₃, and Ag₂S₅.

Structural and relative stabilities, electronic properties, and hardness of iron tetraborides from first prinicples.

First-principles calculations were carried out to investigate the structure, phase stability, electronic property, and roles of metallicity in the hardness for recently synthesized FeB4 with various different structures. Our calculation indicates that the orthorhombic phase with Pnnm symmetry is the most energetically stable one. The other four new dynamically stable phases belong to space groups monoclinic C2/m, orthorhombic Pmmn, trigonal R3̅m, and hexagonal P63/mmc.

Phase stability, mechanical properties, hardness, and possible reactive routing of chromium triboride from first-principle investigations.

The first-principles calculations are employed to provide a fundamental understanding of the structural features and relative stability, mechanical and electronic properties, and possible reactive route for chromium triboride. The predicted new phase of CrB3 belongs to the rhombohedral phase with R-3m symmetry and it transforms into a hexagonal phase with P-6m2 symmetry at 64 GPa. The mechanical and thermodynamic stabilities of CrB3 are verified by the calculated elastic constants and formation enthalpies.

Probing the structural, bonding, and magnetic properties of cobalt coordination complexes: co-benzene, co-pyridine, and co-pyrimidine.

Neutral and anionic Co1,2(benzene)1,2, Co1,2(pyridine)1,2, and Co1,2(pyrimidine)1,2 complexes have been investigated within the framework of an all-electron gradient-corrected density functional theory. The ground-state structures for each size clusters were identified based on the geometry optimization. Meanwhile, their electron affinities and vertical detachment energies were predicted and compared with the experimental values.

Formation and properties of iron-based magnetic superhalogens: a theoretical study.

In order to explore new magnetic superhalogens, we have systematically investigated the structures, electrophilic properties, stabilities, magnetic properties, and fragmentation channels of neutral and anionic Fe(m)F(n) (m = 1, 2; n = 1-7) clusters using density functional theory. Our results show that a maximum of six F atoms can be bound atomically to one Fe atom, and the Fe-Fe bonding is not preferred in Fe2F(n)(0/-) clusters. The computed electron affinities (EAs) indicate that FeF(n) with n ≥ 3 are superhalogens, while Fe2F(n) can be classified as superhalogens for n ≥ 5.

Structures, electrophilic properties, and hydrogen bonds of cytidine, uridine, and their radical anions: Microhydration effects.

Structures, electrophilic properties, and hydrogen bonds of the neutral and anionic monohydrated nucleoside, (cytidine)H2O, and (uridine)H2O have been systematically investigated using density functional theory. Various water-binding sites were predicted by explicitly considering the optimized monohydrated structures. Meanwhile, predictions of electron affinities and vertical detachment energies were also carried out to investigate their electrophilic properties.

Evolution of structure and properties of neutral and negatively charged transition metal-coronene complexes: a comprehensive analysis.

The geometries, electronic and magnetic properties of neutral and negatively charged Mn(coronene)m (M = V and Ti; n, m = 1, 2) complexes were investigated using density functional theory. The results show that one V or Ti atom prefers to occupy the η(6)-site in M(coronene)(0/-) complexes and to be sandwiched between the two coronene molecules in M(coronene)2(0/-) complexes. Two metal atoms always form a dimer and interact with one coronene molecule.

Probing the structural, electronic and magnetic properties of multicenter Fe₂S₂⁰/⁻, Fe₃S₄⁰/⁻ and Fe₄S₄⁰/⁻ clusters.

The structural, electronic and magnetic properties of neutral and anion Fe2S2, Fe3S4 and Fe4S4 have been investigated with the aid of previous photoelectron spectroscopy and density functional theory calculations. Theoretical electron detachment energies (both vertical and adiabatic) of anion clusters for the lowest energy structure were computed and compared with the experimental results to verify the ground states. The optimized structures show that the ground state structures of Fe2S2(0/-), Fe3S4(0/-) and Fe4S4(0/-) favor high spin state and are similar to their structures in proteins.

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.

Probing the structural and electronic properties of aluminum-sulfur AlnSm (2≤n+m≤6) clusters and their oxides.

Using the first-principle density functional calculations, the equilibrium geometries and electronic properties of anionic and neutral aluminum-sulfur AlnSm (2≤n+m≤6) clusters have been systematically investigated at B3PW91 level. The optimized results indicate that the lowest-energy structures of the anionic and neutral AlnSm clusters prefer the low spin multiplicities (singlet or doublet) except the Al2‾, Al2, S2, Al4 and Al2S4 clusters. A significant odd-even oscillation of the highest occupied-lowest unoccupied molecular orbital (HOMO-LUMO) energy gaps for the AlnSm‾ clusters is observed.

Theoretical investigation on the structural and thermodynamic properties of FeSe at high pressure and high temperature.

A theoretical investigation on structural and thermodynamic properties of 11-type iron-based superconductor FeSe at high pressure and high temperature was performed by employing the first-principles method based on the density functional theory. Some structural parameters of FeSe in both tetragonal and hexagonal phases are reported. According to the fourth-order Birch-Murnaghan equation of states, the transition pressure P(t) of FeSe from the PbO-type phase to the NiAs-type phase was determined.