Free or Quasi-Free Electronic Density of States in a Confined Atom

A new general formula, for energy normalization of radial wave-functions of free electron and of quasi-free electron in confined atom, is derived in central field approximation, which can flexibly be applied to the cases of relativity,non-relativity, and of free atom.     

Quantum Inequality for Negative Energy Density States of Massive Dirac Field in Four-Dimensional Spacetime

Negative energy density and the quantum inequality are examined for the Dirac field. A proof is given of the quantum inequality for negative energy densities in the massive Dirac field produced by the superposition of two single particle electron states.     

First-Principles Study on Elastic Properties and Electronic Structures of Ti-Based Binary and Ternary Shape Memory Alloys

The elastic properties and electronic structure of B2 phase binary TiM （M =Fe, Co, Ni, Pd, Pt and Au） and ternary TisoNi43.75Pd6.25, TisoNi43.75Cu6.25 shape memory alloys are studied by the plane-wave psedudopotential method within the local density approximation. The elastic constants and density of states are calculated. Our calculations show that the martensitic transformation behaviour of these alloys is closely related to their elastic properties. The Ti d DOS at the Fermi level is mainly responsible for the B2 phase stability of these alloys.     

Structure—Depandent Electronic and Optical Properties of the Martensitic Alloys TiAu

The atomic and electronic structures together with the optical properties of TiAu in the low-temperature B19 and B11 phases are calculated by using first principles local density functional approaches.Our results show that the B11 structure is more stable than B19 for the TiAu alloy in ordered equiatomic composition (Ti:Au=50:50).At low temperatures,the B11 structure should exist as a binary alloy from the energetic consideration.The accurate atomic positions in the unit cell have been given by fully force relaxed calculations.The calculated optical conductivities of B19 and B11 phases show a drastic change in the region of 1.5 to 3.5eV.     

Quantum-Mechanical Study of Small Au2Pdn （n=1 ～ 4） Clusters

Gold-doped palladium clusters, Au2Pdn （n=1～4）, are investigated using the density functional method B3LYP with relativistic effective core potentials （RECP） and LANL2DZ basis set. The possible geometrical configurations with their electronic states are determined, and the stability trend is investigated. Several low-lying isomers are determined, and many of them are in electronic configurations with a high-spin multiplicity. Our results indicate that the palladium-gold interaction is strong enough to modify the known pattern of bare palladium clusters, and the lower stability as the structures grow in size. The present calculations are useful to understanding the enhanced catalytic activity and selectivity gained by using gold-doped palladium catalyst.     

First-Principles Study of Electronic Structure of the Laves Phase ZrFe2

We perform the ab initio calculation for obtaining the density of states and magnetic properties of ZrFe2 Laves phase compound based on the method of augmented plane waves plus local orbital The results indicate that the ferromagnetic state is more stable than the paramagnetic one, but with a slightly larger volume. The 3d - 4d exchange interactions between Fe and Zr electrons lead to the antiparallel coupling for Fe 3d and Zr 4d states, which is responsible for the ferrimagnetic ordering of the compound. The resulting magnetic moment of about 1.98μB for Fe is spatially localized near the Fe site, while around Zr a small but extended negative spin states causes a moment of about -0.44 μB. Moreover, the resulting magnetic moments with the generalized gradient approximation are more consistent with experimental values than that of the local-spin density approximation.     

Codoping of Potassium and Bromine in Carbon Nanotubes： A Density Functional Theory Study

We investigate the co-doping of potassium and bromine in single-walled carbon nanotubes （SWCNTs） and doublewalled carbon nanotubes （DWCNTs） based on density functional theory. In the co-doped （6,0） SWCNTs, the 4s electron of potassium is transferred to nanotube and Br, leading to the n-type feature of SWCNTs. When potassium is intercalated into inner tube and bromine is put on outer tube, the positive and negative charges reside on the outer and inner tubes of the （7,0）@（16,0） DWCNT, respectively. It is expected that DWCNTs would be an ideal candidate for p-n junction and diode applications.     

Electronic Structure of One—Dimensional Boron Chains with Density Functional Theory Method

One-dimensional chain structures of Bn(n=6-16) are calculated by employing a 6-311 G^* basis set.The present calculations show that all the chain structures of interest have local minima with large binding energy per atom and short bond length.It is also found that many previous reported structures of B6 and B7 clusters are saddle points and the one-dimensional chain structures are the corresponding ground-state structures of B6 and B7 clusters.     

Equilibrium Properties of Hard Sphere Fluid in Confined Geometries：a Density Functional Theory Study

One component hard-sphere fluid confined in two planar hard wllas is studied by means of density functional theroy with Rosenfeld functional and molecular dynamics simulation,the Validity of the Rosenfeld functional is examined,Chemical potential,grand potential and free energy as functions of the wall separation are obtained.     

Molecular Dynamics Study of Icosahedral Clusters in Ni-Zr Amorphous Alloys

Formation of icosahedral dusters in rapidly solidified binary amorphous NixZr100-x （x = 15, 33.3, 50, 66.7, 85） is studied by using molecular dynamics simulation methods. A large number of icosahedral dusters with 13 atoms （Ih13） were observed in NixZr100-x alloys, and most of them, even those in Zr-rich alloys, are found to be Ni-centred. Studies on the structures of Ni33.3Z66.7 obtained at different cooling rates demonstrate that most of iscosahedral dusters enhanced by decreasing cooling rates are also Ni-centred, The essentials of Ni atoms preferring to be the core of icosahedral clusters are illustrated with the criterion of energy minimization and the equilibrium interatomic distances between different atoms.     

Numerical Study of Luttinger Liquid Regime of Two-Leg Hubbard Ladders

We investigate two-leg Hubbard ladders in the Luttinger liquid regime by the density-matrix renormalization group method. Applicability of the bond concept in this region is discussed in a quantitative comparison of power-law decay exponents, energy components and anti-bond occupations between ladders and chains. The interaction between bond and anti-bond bands induced by finite Hubbard repulsion U is emphasized by our numerical results. Our quantitative results are useful for the justification of the validity of various analytical approaches.     

Ab Initio Study of Structural and Electronic Properties of Hexagonal BC2N

We investigate hexagonal BC2N in graphite unit cells using the first-principles method and calculate the total energies, lattice parameters, and electronic band structures after full relaxation. It is shown that stable hexagonal BC2N should be stacked sequentially with one graphite layer and one h-BN layer. The density of states indicates that this structure should have metallicity.     

Experimental Studies of Liquid Viscosity in Immiscible Al—In Alloys

The liquid viscosity o[ immiscible Al-In alloys was measured using an oscillating-cup viscometer. It has been found that the viscosity of Al-In melts changes abruptly at the critical temperature of liquid-liquid phase separation during the cooling process. The experimental data above the temperature of phase separation are fitted to the Arrhenius equation. The fitted results show that the temperature dependence o[the viscosity obeys the Arrhenius relationship.     

Influence of High Atomic Hydrogenation on the Electronic Structure of Zigzag Carbon Nanotubes： A First-Principles Study

Using density functional theory, we study high hydrogenated zigzag single-walled carbon nanotubes from （7,0） to （11,0）. Two structure transitions are classified： type A is a metallic transition and type B is a ＂semiconductive transition＂ according to the energy band structure. The charge density transforms only at the C-C bonds without hydrogenated sites. The sp^3 hybridization is mainly enhanced for all the C-C bonds in the vertical axial direction for type-A configurations, and the sp^3 hybridization mainly increases for all C-C bonds along the axial direction for the type-B case.     

An Experimental Study of Mg Aggregation in AA5754 Alloys by Positron Annihilation Spectroscopy

Defects in an AA5754 （Al-3.0%Mg） alloy are investigated by coincidence Doppler broadening spectroscopy and positron lifetime spectroscopy. The results indicate enhancement of positron trapping by Mg atoms in this Al-Mg alloy after quenching treatment at 623K, which may be due to the formation of vacancy-Mg complexes or the aggregation of Mg near the vacancy sites. It is speculated that the aggregation of Mg atoms in the moderate temperature range is responsible for cracking in spot welding of AA5754 alloys.     

Ultrafast Imaging of Electronic Relaxation in Ortho-xylene： New Features from Fragmentation-Ion Spectroscopy

After light absorption, a molecule can undergo ra- diationless processes, and photophysics is one of the important general types. The photophysical pro- cesses involve internal conversion （IC） due to elec- tronic nonadiabaticity and intersystem crossing （ISC） induced by spin-orbit coupling. In polyatomic molecules that are excited IC and ISC to vibronic to higher electronic states, levels of lower electronic states are two dominant mechanisms. With the ad- vent of femtosecond ultrashort pulse, tracking and controlling the ultrafast photophysical processes be- come realizable. Due to the fact that ISC requires a change in the spin of an electron, it is usually a slower process than IC. However, extensive reports show that ultrafast competing ISC exists in a number of systems. Re- cently, Richter et al. reported femtosecond ISC in cytosine. Martinez-Fernandez et al. simulated the deactivation dynamics of photo-excited 6-thioguanine using a direct surface hopping dynamics approach Their simulations show that 6-thioguanine is another example of a system showing ultrafast ISC that can compete with IC in the same time scale. Both the spin-orbit and the dynamic couplings are important to describe realistically the excited state dynamics of 6-thioguanine. A similar phenomenon has also been evidenced in the S1 state of benzene. The exper- imental results show that the ultrafast decay of the S1 state is due to competing IC and ISC processes and both processes occur on a femtosecond timescale. Spin-orbit coupling is highly effective when the in- volved states are nearly isoenergetic.     

Coupling of Magnetization and Structural Distortions in Multiferroic BiFeO3： an Ab Initio Density Functional Theory Study

The coupling between magnetism and structural distortions in BiFeO3 （BFO） is investigated using density functional theory by considering the spin-orbit effect. Computational results show that the resulting magnetization M is rotated by reversal of sense of rotation of the oxygen octahedra in the double cell. The resulting magnetization is determined by the antiferrodistortive （AFD） distortions and ferroelectric （FE） displacements. This work clarifies the previous view that magnetism is only coupled with, and determined by, FE displacements. The excellent ferroelectricity is attributed significantly to the anomaly of Born effective charge of Bi, which is caused by the stereochemically active long pair of Bi 6s.     

Thin-Thick Film Transitions on a Planar Solid Surface： A Density Functional Study

A weighted density functional theory is proposed to predict the surface tension and thin-thick film transition of a Lennard-Jones fluid on a planar solid surface. The underlying density functional theory for the Lennard-Jones fluid at low temperature is based on a modified fundamental measure theory for the hard-core repulsion, a Taylor expansion around zero-bulk-density for attraction, and a correlation term evaluated by the weighted density approximation with a weight function of the Heaviside step function. The predicted surface tension and thin-thick film transition agree well with the results from the Monte Carlo simulations, better than those from alternative approaches. For the Ar/CO2 system, the prewetting line has been calculated. The predicted reduced surface critical temperature is about 0.97, and the calculated wetting temperature is below the triple-point temperature. This is in agreement with the experimental observation.     

Relativistic Multichannel Theory：Theoretical Study of C^＋ Autoionization States

Based on relativistic multichannel theory,the autoionization states of C are studied.We calculate all the autoionization states in the energy region of 193900-231700cm^-1,and the results are in good agreement with the experimental data.The energy structure we obtain will be important in the dielectronic recombination processes,which plays a key role in determining the abundance of carbon in a nebula.     

Non-Local Density Functional Description of Poly-Para-Phenylene Vinylene

A fully non-local exchange-correlation formalism the weighted density approximation （WDA）, has within the framework of density functional theory, known as been applied to the conjugated polymer poly-para-phenylene vinylene （PPV） and is shown to lead to a marked improvement in the agreement of theory and experiment for the electronic band structure of the conjugated polymer. In particular, some new model WDA functions are developed, which substantially increase the electronic band gap of the polymer relative to those obtained with the local density approximation and generalized gradient approximation. The calculated band gap of PPV is quantitatively or atleast semiquantitatively in agreement with the experimental data.