Su-Juan Wang

Equilibrium Geometries, Stabilities, and Electronic Properties of the Bimetallic M2-doped Aun (M = Ag, Cu; n = 1−10) Clusters: Comparison with Pure Gold Clusters

The density functional method with relativistic effective core potential has been employed to investigate systematically the geometrical structures, relative stabilities, growth-pattern behaviors, and electronic properties of small bimetallic M(2)Au(n) (M = Ag, Cu; n = 1-10) and pure gold Au(n) (n ≤ 12) clusters. The optimized geometries reveal that M(2) substituted Au(n+2) clusters and one Au atom capped M(2)Au(n-1) structures are dominant growth patterns of the stable alloyed M(2)Au(n) clusters. The calculated averaged atomic binding energies, fragmentation energies, and the second-order difference of energies as a function of the cluster size exhibit a pronounced even-odd alternation phenomenon. The analytic results exhibit that the planar structure Ag(2)Au(4) and Cu(2)Au(2) isomers are the most stable geometries of Ag(2)Au(n) and Cu(2)Au(n) clusters, respectively. In addition, the HOMO-LUMO gaps, charge transfers, chemical hardnesses and polarizabilities have been analyzed and compared further.

Geometries, Stabilities, and Electronic Properties of Small Anion Mg-Doped Gold Clusters: A Density Functional Theory Study

First-principle density functional theory is used for studying the anion gold clusters doped with magnesium atom. By performing geometry optimizations, the equilibrium geometries, relative stabilities, and electronic and magnetic properties of [Au(n)Mg]⁻ (n = 1-8) clusters have been investigated systematically in comparison with pure gold clusters. The results show that doping with a single Mg atom dramatically affects the geometries of the ground-state Au(n+1)⁻ clusters for n = 2-7. Here, the relative stabilities are investigated in terms of the calculated fragmentation energies, second-order difference of energies, and highest occupied−lowest unoccupied molecular orbital energy gaps, manifesting that the ground-state [Au(n)Mg]⁻ and Au(n+1)⁻ clusters with odd-number gold atoms have a higher relative stability. In particular, it should be noted that the [Au₃Mg]⁻ cluster has the most enhanced chemical stability. The natural population analysis reveals that the charges in [Au(n)Mg]⁻ (n = 2-8) clusters transfer from the Mg atom to the Au frames. In addition, the total magnetic moments of [Au(n)Mg]⁻ clusters exhibit an odd-even oscillation as a function of cluster size, and the magnetic effects mainly come from the Au atoms.

Ab initio calculation of the geometries, stabilities, and electronic properties for the bimetallic Be2Au(n) (n = 1-9) clusters: comparison with pure gold clusters.

Ab initio methods based on density functional theory at BP86 level were applied to the study of the geometrical structures, relative stabilities, and electronic properties of small bimetallic Be2Aun (n = 1–9) clusters. The optimized geometries reveal that the most stable isomers have 3D structures at n = 3, 5, 7, 8, and 9. Here, the relative stabilities were investigated in terms of the averaged atomic binding energies, fragmentation energies and second-order difference of energies. The results show that the planar Be2Au4 structure is the most stable structure for Be2Aun clusters. The HOMO−LUMO gap, vertical ionization potential, vertical electron affinity and chemical hardness exhibit a pronounced even–odd alternating phenomenon. In addition, charge transfer and natural electron configuration were analyzed and compared.

Equilibrium geometries, stabilities, and electronic properties of the cationic AunBe+ (n=1-8) clusters: comparison with pure gold clusters

Ab initio method based on density functional theory at PW91PW91 level has been applied in studying the geometrical structures, relative stabilities, and electronic properties of small bimetallic AunBe+ (n = 1–8) cluster cations. The geometrical optimizations indicate that a transition point from preferentially planar (two-dimensional) to three-dimensional (3D) structures occurs at n = 6. The relative stabilities of AunBe+ clusters for the ground-state structures are analyzed based on the averaged binding energies, fragmentation energies, and second-order difference of energies. The calculated results reveal that the AuBe+ and Au5Be+ clusters possess higher relative stability for small size AunBe+ (n = 1–8) clusters. The HOMO-LUMO energy gaps as a function of the cluster size exhibit a pronounced even-odd alternation phenomenon. Sequently, the natural population analysis and polarizability for our systems have been analyzed and compared further.

A systematic search for the structures, stabilities, and electronic properties of bimetallic Ca 2 -doped gold clusters: comparison with pure gold clusters

The local meta-GGA exchange correlation density functional (TPSS) with a relativistic effective core potential was employed to systematically investigate the geometric structures, stabilities, and electronic properties of bimetallic Ca2Aun (n = 1–9) and pure gold Aun (n ≤ 11) clusters. The optimized geometries show that the most stable isomers for Ca2Aun clusters have 3D structure when n > 2, and that one Au atom capping the Ca2Aun−1 structure for different-sized Ca2Aun (n = 1–9) clusters is the dominant growth pattern. The average atomic binding energies and second-order difference in energies show that the Ca2Au4 isomer is the most stable among the Ca2Aun clusters. The same pronounced even–odd alternations are found in the HOMO–LUMO gaps, VIPs, and hardnesses. The polarizabilities of the Ca2Aun clusters show an obvious local minimum at n = 4. Moreover, the inverse corrections to the polarizabilities versus the ionization potential and hardness were found for the gold clusters.

Theoretical investigation on the high-pressure structural transition and thermodynamic properties of cadmium oxide

A theoretical investigation on the structural and thermodynamic properties of CdO under high pressure is performed by employing the pseudopotential plane-wave method in the framework of the density functional theory. Some structural parameters of CdO in both B1 and B2 phases are reported. According to the third-order Birch-Murnaghan equation of states, the transition pressure P(t) of CdO from the B1 structure to the B2 structure is determined. The calculated results are found to be in good agreement with the available experimental data and theoretical values. Based on the quasi-harmonic Debye model, the Debye temperature of CdO under high pressure is derived from the average sound velocity. This is a quantitative theoretical prediction of the elastic and thermodynamic properties of CdO and it still awaits experimental confirmation. Copyright (C) EPLA, 2010

Squeezing survival and transfer in single and double electromagnetically induced transparency

We investigate the propagation and storage of a squeezed vacuum as the probe light in a collection of N four-level tripod configuration atoms under the condition of single or double electromagnetically induced transparency (EIT). The squeezing of the probe light is well preserved in both the single transparency channel and the double transparency one. On the other hand, the effects of the ground state dephasing rates on the propagation and storage of the squeezed vacuum are investigated. It is found that the maximum squeezing at the transparency points is suppressed by the dephasing rates in single or double EIT. Meanwhile, the mapping of the squeezing of the probe light onto the atomic ground coherences or onto the two atomic dark-state polaritons is also studied. In the absence of the Langevin atomic noise, the quasi-ideal squeezing transfer between the squeezed vacuum and the atomic ground coherences or the dark-state polaritons can be realized in such a system. When considering the Langevin atomic noise, the quantum characteristics of the atomic coherences at resonance are submerged by the Langevin noise, while in the scenario of the dark-state polariton, it is found that squeezing transfer onto one polariton is damaged, but the squeezing transfer onto the other polariton survives even in the presence of the Langevin noise.

Effects of vacuum-induced coherence on dispersion and absorption properties in a tripod-scheme atomic system

When the interactions of the two coupling transitions from an excited level to two nearly degenerate ground levels with the same vacuum occur in a four-level tripod-scheme atomic system, vacuum-induced coherence (VIC) results from the quantum interference between the two spontaneous transitions. We investigate the effects of VIC and the relative phase between the two coupling fields on the probe absorption and dispersion properties as well as the group velocity of the probe field. We find that by adjusting the incoherent pumping field and VIC as well as the relative phase, the central absorption peak in the double transparency spectrum reduces, even develops into a gain dip, and the probe field propagates at a velocity from superluminal to subluminal. It is particularly pointed out that the subluminal light propagation with gain without inversion can be realized in such a system. The physical interpretation of the phenomena has been given.

Theoretical study of local structure for Ni2+ ions at tetragonal sites in K2ZnF4:Ni2+ system.

A theoretical method for studying the local lattice structure of Ni2+ ions in (NiF6)(4-) coordination complex is presented. Using the ligand-field model, the formulas relating the microscopic spin Hamiltonian parameters with the crystal structure parameters are derived. Based on the theoretical formulas, the 45 x 45 complete energy matrices for d8 (d2) configuration ions in a tetragonal ligand-field are constructed. By diagonalizing the complete energy matrices, the local distortion structure parameters (R perpendicular and R || ) of Ni2+ ions in K2ZnF4:Ni2+ system have been investigated. The theoretical results are accorded well with the experimental values. Moreover, to understand the detailed physical and chemical properties of the fluoroperovskite crystals, the theoretical values of the g factor of K2ZnF4:Ni2+ system at 78 and 290 K are reported first.

Equilibrium Geometries, Stabilities, and Electronic Properties of the Bimetallic Ag2-doped Sin (n=1 – 11) Clusters: A Density-Functional Investigation

An ab initio method based on the density functional theory has been employed to investigate the behaviours of the bimetallic Ag2-doped silicon clusters at a size of n = 1 - 11. The possible geometrical configurations, growth-pattern behaviours, stabilities, energy gaps, and electronic properties are presented and discussed. The optimized geometries reveal that the silicon atom surface-capped and silver atom substituted 3D structures are dominant growth patterns. The calculated averaged binding energy, fragmentation energy, and the second-order difference of energy manifest that the most stable structures of Ag2Sin (n = 1 - 11) clusters are Ag2Si2 and Ag2Si5 isomers, which is in qualitative agreement with the AgSin clusters. In addition, the gap between highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) exhibits that the Ag2Si3 and Ag2Si5 isomers have dramatically enhanced chemical stability. Natural population analysis shows that the charge-transfer phenomena are coincidence with the AgSin clusters but different from Mo2Sin systems. Furthermore, the dipole moments of stable Ag2Sin (n = 1 - 11) display a pronounced odd-even oscillation with the number of silicon atoms.