The electronic density of states (DOS) and magnetic moments of rare-earth antimonides (NdVSb3) has been studied by the first principles full-potential linearized augmented plane wave (FP-LAPW) method based on density functional theory (DFT). For the exchange-correlation potential, the GGA+U method is used. The effective moments of NdVSb 3 B was found to be 4.50 . The exchange-splittings of V-3d state electrons and 4f-states of Nd atoms were analyzed to explain the magnetic nature of these systems. The V atom plays a significant role on the magnetic properties due to the hybridization between V-3d and Sb-5p state orbitals. The results obtained are compared and found to be in qualitative agreement with the available results.

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A First Principles Study

Curved pi-conjugation, aromaticity, and the related chemistry of small fullerenes (< C60) and single-walled carbon nanotubes.

Modeling concepts for intermetallic titanium aluminides

Discoveries in quantum materials, which are characterized by the strongly quantum-mechanical nature of electrons and atoms, have revealed exotic properties that arise from correlations. It is the p...

Quantum Information and Algorithms for Correlated Quantum Matter.

Machine learning methods have proved to be useful for the recognition of patterns in statistical data. The measurement outcomes are intrinsically random in quantum physics, however, they do have a pattern when the measurements are performed successively on an open quantum system. This pattern is due to the system-environment interaction and contains information about the relaxation rates as well as non-Markovian memory effects. Here we develop a method to extract the information about the unknown environment from a series of projective single-shot measurements on the system (without resorting to the process tomography). The method is based on embedding the non-Markovian system dynamics into a Markovian dynamics of the system and the effective reservoir of finite dimension. The generator of Markovian embedding is learned by the maximum likelihood estimation. We verify the method by comparing its prediction with an exactly solvable non-Markovian dynamics. The developed algorithm to learn unknown quantum environments enables one to efficiently control and manipulate quantum systems.

Machine Learning Non-Markovian Quantum Dynamics.

The effects of surface self-segregation on the adsorption of oxygen on the $\ensuremath{\gamma}\text{-TiAl}(111)$ surface are investigated by density-functional theory calculations. The oxygen binding-energy results show that on the pure $\ensuremath{\gamma}\text{-TiAl}(111)$ surface, the most stable adsorption sites of oxygen atoms are the sites with more Ti sites as their neighbors, which is in agreement with previous calculations. The defect formation energies and the relative surface energies as functions of chemical potential of Al are calculated. Furthermore, the phase diagram of $\ensuremath{\gamma}\text{-TiAl}(111)$ surfaces with different defects and different oxygen coverage is also calculated. The calculated results show that Al atom can segregate at the $\ensuremath{\gamma}\text{-TiAl}(111)$ surface. Especially, at high Al chemical potential, the first surface layer of the $\ensuremath{\gamma}\text{-TiAl}(111)$ surface can be composed of Al atoms. In this case, the oxygen adsorption behavior is very similar to the case of Al(111) surface: the binding energy per oxygen atom decreases with the increase in the oxygen coverage due to an attractive interaction between O atoms. These results show that the occurrence of Al self-segregation at the $\ensuremath{\gamma}\text{-TiAl}(111)$ surface can enhance the interaction between O and Al atoms. The Al surface segregation effect may be the reason why the growth of pure alumina layer resulting from the selective oxidation of aluminum formed on $\ensuremath{\gamma}\text{-TiAl}(111)$ surface at the first stage in the experiments.

Ab initio study of surface self-segregation effect on the adsorption of oxygen on the γ-TiAl(111) surface

The electronic structures of the molecule ${\mathrm{C}}_{50}{\mathrm{Cl}}_{10}$ are studied in the framework of density functional theory (DFT) with the Perdew-Burke-Ernzerhof (PBE) functional. The static polarizability $\ensuremath{\alpha}$ and second-order hyperpolarizability $\ensuremath{\gamma}$ are calculated by the use of a finite field approach. Both the average static polarizability $(⟨\ensuremath{\alpha}⟩=92.9\phantom{\rule{0.3em}{0ex}}{\mathrm{\AA{}}}^{3})$ and the second hyperpolarizability $(⟨\ensuremath{\gamma}⟩=83.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}36}\phantom{\rule{0.3em}{0ex}}\mathrm{esu})$ are larger than those of ${\mathrm{C}}_{60}$. At the same time, the diagonal components of $\ensuremath{\alpha}$, especially the $\ensuremath{\gamma}$ in the $xy$ plane, which contains the Cl atoms, are much larger than those in the $z$ direction. The reason is mainly from the distribution of $\ensuremath{\pi}$ electrons of the HOMO in the planes perpendicular to the $z$ axis. We predict that ${\mathrm{C}}_{50}{\mathrm{Cl}}_{10}$ and its derivatives should be promising nonlinear optical materials.

Density functional calculations of the polarizability and second-order hyperpolarizability of C 50 Cl 10

We perform first-principles calculations based on the density-functional theory to study the surface segregation of Si and its effect on the oxygen adsorption on a γ-TiAl(111) surface for a range of oxygen coverage 0<Θ≤1.0 monolayer (ML). The calculated results show that the alloying Si atoms prefer occupying surface Ti sites to the sites in the bulk of γ-TiAl, which suggests the occurrence of Si surface segregation. When oxygen atoms adsorb on a pure γ-TiAl(111) surface, the most favorable sites are the adsorption sites with more Ti atoms as their nearest neighbors in the surface layer at all the calculated coverages and the interactions between adsorbed oxygen atoms are repulsive. However, when oxygen atoms adsorb on an Si-alloyed γ-TiAl(111) surface, the interactions between the adsorbed oxygen atoms are attractive at oxygen coverage 0<Θ≤1.0 ML. Meanwhile, the interactions between O and Al atoms become stronger whereas those between O and Ti atoms become weaker relative to oxygen adsorbed on a pure γ-TiAl(111) surface. The atomic geometry and density of state are analyzed. The results show that the surface ripple of the top metal layer for oxygen on a pure γ-TiAl(111) surface is Ti upwards, while that for oxygen on an Si-alloyed γ-TiAl(111) surface is Al upwards at high oxygen coverage (Θ≥0.50 ML). This effect of Si is of benefit to the nucleation of alumina, which is attributed to Si surface segregation and an increase of the surface Al:Ti ratio. This can help to explain why alloying the γ-TiAl(111) surface with Si could favor the formation of the Al2O3 scale at the first stage and result in good oxidation resistance in experiments.

https://iopscience.iop.org/article/10.1088/0953-8984/21/22/225005/pdf

Surface segregation of Si and its effect on oxygen adsorption on a γ-TiAl(111) surface from first principles.

Quantum entanglement, the essential resource for quantum information processing, has rich dynamics under different environments. Probing different entanglement dynamics typically requires exquisite control of complicated system-environment coupling in real experimental systems. Here, by a simple control of the effective solid-state spin bath in a diamond sample, we observe rich entanglement dynamics, including the conventional asymptotic decay as well as the entanglement sudden death, a term coined for the phenomenon of complete disappearance of entanglement after a short finite time interval. Furthermore, we observe counterintuitive entanglement rebirth after its sudden death in the same diamond sample by tuning an experimental parameter, demonstrating that we can conveniently control the non-Markovianity of the system-environment coupling through a natural experimental knob. Further tuning of this experimental knob can make the entanglement dynamics completely coherent under the same environmental coupling. Probing of entanglement dynamics, apart from its fundamental interest, may find applications in quantum information processing through control of the environmental coupling.

Observation of entanglement sudden death and rebirth by controlling a solid-state spin bath

We calculate the lifetime distribution function of an assembly of polarized atoms in two-dimensional (2D) photonic crystals (PCs) at different polarization orientations of atomic dipole moments. We reveal a switching effect of atomic spontaneous emission (SE) and find a significant change of atomic lifetime, up to a factor of 33, by tuning the polarized orientation of the atoms. These observations suggest that the tuning of the polarized orientation of atoms provides a new way for the effective control of atomic SE processes in 2D PCs.

Fu-He Wang

Papers

Ab initio study of surface self-segregation effect on the adsorption of oxygen on the γ-TiAl(111) surface

Density functional calculations of the polarizability and second-order hyperpolarizability of C 50 Cl 10

Surface segregation of Si and its effect on oxygen adsorption on a γ-TiAl(111) surface from first principles.

Observation of entanglement sudden death and rebirth by controlling a solid-state spin bath

Switching Control of Spontaneous Emission by Polarized Atoms in Two-Dimensional Photonic Crystals