Global dynamical analysis of vibrational manifolds of HOCl and HOBr under anharmonicity and Fermi resonance:the dynamical potential approach

The vibrational dynamics of HOCl and HOBr between bending and OCl/OBr stretching coordinates with anharmonicity and Fermi coupling is studied with the classical dynamical potential approach. The quantal vibrational dynamics is mostly mapped out by the classical nonlinear variables such as fixed points, except for the state energies, which are quantized. This approach is global in the sense that the focus is on a set of levels instead of individual ones. The dynamics of HOBr is demonstrated to be less complicated. The localized modes along the OCl/OBr stretching coordinates are also shown to have O-Br bonds more prone to dissociation.     

Bending localization of nitrous oxide under anharmonicity and Fermi coupling: the dynamical potential approach

This paper studies the vibrational nonlinear dynamics of nitrous oxide with Fermi coupling between the symmetric stretching and bending coordinates by classical dynamical potential approach.This is a global approach in the sense that the overall dynamics is evidenced by the classical nonlinear variables such as the fixed points and the focus are on a set of levels instead of individual ones.The dynamics of nitrous oxide is demonstrated to be not so much dependent on the excitation energy.Moreover,the localized bending mode is shown to be ubiquitous in all the energy range studied.     

HOCl分子高激发振动态的动力学势研究

通过研究HOCl分子高激发振动态的动力学势, 明确了该体系的动力学特点. 研究表明, 在O-Cl伸缩模式和H-O-Cl弯曲模式间存在2:1 Fermi共振的动力学模型下, H-O伸缩振动模式对于上述两种振动模式的动力学势有显著影响, 且这种影响随Polyad数呈现有规律的变化. 作为定量研究, 还研究了Polyad数为24时该分子体系的动力学势与各能级的相空间轨迹. 分析表明, 相空间轨迹与动力学势中的动力学不动点有很好的对应关系. 此外, 将该Polyad数下的动力学势中的能级按照相空间轨迹的作用量积分进行分类, 明确了这些能级所处的量子环境.     

Single-particle spectral density of the unitary Fermi gas: Novel approach based on the operator product expansion,sum rules and the maximum entropy method

Making use of the operator product expansion, we derive a general class of sum rules for the imaginary part of the single-particle self-energy of the unitary Fermi gas. The sum rules are analyzed numerically with the help of the maximum entropy method, which allows us to extract the single-particle spectral density as a function of both energy and momentum. These spectral densities contain basic information on the properties of the unitary Fermi gas, such as the dispersion relation and the superfluid pairing gap, for which we obtain reasonable agreement with the available results based on quantum Monte-Carlo simulations.     

Energy spectra of three‐dimensional harmonium under Debye potential obtained using the shifted 1/N expansion approach

In this work, the problem of harmonium was investigated using the method of the shifted 1/N expansion. The energy eigenvalues and the classical equilibrium interelectron distance were calculated for ground and few first excited states under Debye potential as a function of both the Debye screening length and the harmonic confinement strength. It was found that harmonium becomes a Wigner molecule at the strong‐correlation limit in which the two electrons oscillate about the classical equilibrium interelectron distance r₀ . The results show reasonable agreement with the previous results both quantitatively and qualitatively.     

Solutions of the two-body Salpeter equation under the Coulomb and exponential potential for any l state with Laplace approach

In this paper we have solved the two-body spinless-Salpeter (SS) equation under the Coulomb and exponential type potentials. We have applied an approximation for the centrifugal term in our calculations. The energy eigenvalues and the corresponding eigenfunctions are reported by using the Laplace transform approach for any n, l states.     

Phase transition,lattice dynamical and thermodynamic properties of yttrium antimonide with the rock salt structure under high pressure: first-principles investigations

We investigate the structural, electronic, first-order pressure-induced phase transition, lattice dynamical, and thermodynamic properties of yttrium antimonide (YSb) with the rock salt structure at high pressures and high temperatures using the projector-augmented wave method based on the density-functional theory. By the usual condition of equal enthalpy, we find that the rock salt-structured YSb is stable up to 31.10 GPa, and then transforms to the CsCl-type structure, this is consistent with the experiment result which begins transform from 26 GPa then ends at 36 GPa. The phonon dispersion curves of the rock salt-structured YSb are calculated under high pressure for the first time using a linear-response approach to density-functional perturbation theory successfully. Within the calculated phonon density of state and the quasi-harmonic approximation, we predict further the thermal physical properties of YSb under high temperature and high pressure systematically.     

Self-consistent Shaw optimized model potential: Application to the determination of structural and atomic transport properties of liquid alkali metals by molecular dynamics simulations

The ‘first-principles’ fully non-local and energy-dependent optimized model potential (OMP) derived by Shaw is developed further. In contrast to Shaw's original paper, OMP parameters are derived in a self-consistent manner that does not rely on knowledge of experimental values of the ionization and cohesive energies. To our knowledge, this is the first time that this method has been used for effective potential calculations. In an application to liquid Li, Na, and K alkali metals, we used OMP pseudopotential-based interactions between ions to carry out standard molecular dynamics simulations. In the calculations, the ionic structure for the liquid state was first checked at a temperature near the melting point. Similar accurate calculations, but for atomic transport properties, predict the temperature dependence of the self-diffusion coefficients. The theoretical results obtained are in overall agreement with available experimental measurements. Thus, one can have some confidence in the ability of the optimized model potential to give a good representation of the physical properties of these alkali ions in the liquid environment.     

Theoretical insight into the influence of molecular ratio on the binding energy and mechanical property of HMX/2-picoline-N-oxide cocrystal,cooperativity effect and surface electrostatic potential

Molecular dynamics method was employed to study the binding energies and mechanical properties of the selected crystal planes of the energetic/nonenergetic 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX)/2-picoline-N-oxide cocrystal in different molecular ratios. The solvent effect in HMX:2-picoline-N-oxide (1:1) was calculated, and the cooperativity effect was discussed in HMX···HF/CH₄···2-picoline-N-oxide by using the M06-2X and MP2(full) methods at the 6-311++G^** basis set. The density, oxygen balance and detonation velocity were calculated. The results indicate that HMX/2-picoline-N-oxide prefers cocrystalising in the 1:1, 2:1 and 3:1 molar ratios, in which the cocrystals own the highest binding energy and best ductility. The cooperativity effect is present in the cyclic complex with CH₄, while the anti-cooperativity effect is found in the HF complex. Thus, in order to obtain stable HMX/2-picoline-N-oxide cocrystal, the solvent with low dielectric constant should be chosen, as is in accordance with the result from solvent effect. The reduced density gradient (RDG) and surface electrostatic potential analysis confirms the cooperativity effect and reveals the nature of decreased sensitivity in complex (or cocrystal). The cocrystals in the molar ratios of 5:1–10:1 could be satisfactory in view of explosive properties.     

Frequency-dependent linear and non-linear response properties of single carrier quantum dots: Role of effective mass and anharmonicity in the confinement potential

We explore the pattern of frequency-dependent linear and non-linear optical (NLO) response of one electron quantum dots harmonically confined in two dimensions. For some fixed values of transverse magnetic field strength (ω_c), and harmonic confinement potential (ω₀), the influence of effective mass (m^*) of the system and the symmetry breaking anharmonic interaction on the frequency-dependent linear (α), and the first (β), and second (γ) NLO responses of the dot is computed through linear variational route. The investigation reveals interesting roles played by the anharmonic interaction and effective mass in modulating the response properties.     

Global dynamics of a pipe conveying pulsating fluid in primary parametrical resonance: Analytical and numerical results from the nonlinear wave equation

The chaotic dynamics of nonlinear waves in the harmonic-forced fluid-conveying pipe in primary parametrical resonance, is explored analytically and numerically. The multiple scale method is applied to obtain an equivalent nonlinear wave equation from the complicated nonlinear governing equation describing the fluid conveyed in a pipe. With the Melnikov method, the persistence of a heteroclinic structure is shown to be satisfied and its condition is given in functional form. Similarly, for the heteroclinic orbit, using geometric analysis, a condition function of the stable manifold is derived for the orbit to return to the stable manifold from the saddle point. The persistent homoclinic structures and threshold of chaos in the Smale-horseshoe sense are obtained for the fluid-conveying pipe under both conditions, indicating how the external excitation amplitude can change substantially the global dynamics of the fluid conveyed in the pipe. A numerical approach was used to test the prediction from theory. The impact of the external excitation amplitude on the nonlinear wave in the fluid-conveying pipe was also studied from numerical simulations. Both theoretical predications and numerical simulations attest to the complex chaotic motion of fluid-conveying pipes.