Effective Hamiltonian for scalar theories in the Gaussian approximation

We use a Gaussian wave functional for the ground state to reorder the Hamiltonian into a free part with a variationally determined mass and the rest. Once spontaneous symmetry breaking is taken into account, the residual Hamiltonian can, in principle, be treated perturbatively. In this scheme we analyze the O(1) and O(2) scalar models. For the O(2)-theory we first explicitly calculate the massless Goldstone excitation and then show that the one-loop corrections of the effective Hamiltonian do not generate a mass.     

The variational iteration method for solitary patterns solutions of gBBM equation

We consider solitary patterns solutions of generalized Benjamin–Bona–Mahony equations (shortly gBBM). The variational iteration method (shortly VIM) is applied for the numerical solution subject to appropriate initial condition. The numerical solutions of our model equation are calculated in the form of convergence power series with easily computable components. The VIM performs extremely well in terms of accuracy, efficiently, simplicity, stability and reliability.     

过渡金属掺杂ZnO的电子结构和光学性质

利用基于密度泛涵理论的超软赝势法(USPP)，结合局域密度近似(LDA)，对过渡族金属离子掺杂的纤锌矿型ZnO做第一性原理计算，得到了它的平衡晶格常数、结合能、电子态密度分布、能带结构、介电函数、光学吸收系数等性质，详细讨论了掺杂后ZnO化合物的电子结构及成键情况，并结合实验结果定性分析了掺杂后光学性质的变化. 关键词： 氧化锌 掺杂 第一性原理 光学性质     

Optimized t-expansion method for the Rabi Hamiltonian

A polemic arose recently about the applicability of the t-expansion method to the calculation of the ground state energy E₀ of the Rabi model. For specific choices of the trial function and very large number of involved connected moments, the t-expansion results are rather poor and exhibit considerable oscillations. In this Letter, we formulate the t-expansion method for trial functions containing two free parameters which capture two exactly solvable limits of the Rabi Hamiltonian. At each order of the t-series, E₀ is assumed to be stationary with respect to the free parameters. A high accuracy of E₀ estimates is achieved for small numbers (5 or 6) of involved connected moments, the relative error being smaller than ¹⁰−4 (0.01%) within the whole parameter space of the Rabi Hamiltonian. A special symmetrization of the trial function enables us to calculate also the first excited energy E₁, with the relative error smaller than ¹⁰−2 (1%).     

First principles study of structural,phonon, optical,elastic and electronic properties of Y3Al5O12

Structural, phonon, optical, elastic and electronic properties of Y₃Al₅O₁₂ have been investigated by means of the first principles method with the Cambridge Serial Total Energy Package (CASTEP) code based on the density functional theory. The calculated lattice parameters, valence charge density, bond length and single crystal elastic properties at zero pressure are in good agreement with the available experimental data. The close agreement with the experimental values provides a good confirmation of the reliability of the calculations. Optical, elastic and phonon properties of Y₃Al₅O₁₂ under pressures are performed. The results that are obtained show the changes of optical and elastic properties under the influence of applied pressure, and proving the dynamical stability of YAG are destructed when applied pressure up to 7 GPa. Moreover, polycrystalline elastic moduli are deduced according to the Reuss assumption. Those elastic constants provide important parameters that describe reliability of both physical model and engineering application at the atomistic level. The result of the density of states explains the nature of the electronic band structure.     

Phase stability,elastic, electronic,thermal and optical properties of Ti3Al1−xSixC2 (0≤x≤1): First principle study

The structural parameters with stability upon Si incorporation and elastic, electronic, thermodynamic and optical properties of Ti₃Al_1−xSi_xC₂ (0≤x≤1) are investigated systematically by the plane wave pseudopotential method based on the density functional theory (DFT). The increase of some elastic parameters with increasing Si-content renders the alloys to possess higher compressive and tensile strength. The Vickers hardness value obtained with the help of Mulliken population analysis increases as x is increased from 0 to 1. The solid solutions considered are all metallic with valence and conduction bands, which have a mainly Ti 3d character, crossing the Fermi level. The temperature and pressure dependences of bulk modulus, normalized volume, specific heats, thermal expansion coefficient, and Debye temperature are all obtained through the quasi-harmonic Debye model with phononic effects for T=0−1000 K and P=0−50 GPa. The obtained results are compared with other results available. Further an analysis of optical functions for two polarization vectors reveals that the reflectivity is high in the visible–ultraviolet region up to ∼10.5 eV region showing promise as a good coating material.     

The structural and electronic properties of silicon nanoribbons on Ag(110): A first principles study

We have investigated the structures of silicon nanoribbons on Ag(110) using first principles calculations. The armchair silicon nanoribbons (ASiNRs) and zigzag silicon nanoribbons (ZSiNRs) with different widths are analyzed. The formation energy study shows that the ASiNRs with the width of 16 Å are the most stable structures. These ASiNRs have the structural parameters same as experimental ones. The simulated scanning tunneling microscope (STM) images of these ASiNRs also agree well with the experimental results. Thus, these ASiNRs are supposed to be the nanoribbons grown in experiment. The electronic structures shows that the ASiNRs are metallic, which is in agreement with the experiments.     

Oscillator strengths and polarizabilities of the hot-dense plasma-embedded helium atom

The effect of weakly coupled hot plasma environment on the oscillator strengths of the ultraviolet and visible series and the polarizabilities of helium has been investigated using variational highly correlated wave functions within the non-relativistic framework. The Debye shielding approach that admits a variety of plasma conditions is used to simulate the plasma effects. For each shielding parameter, dipole oscillator strengths are calculated for the 1 ¹S-n¹P (n=2, 3), 2 ¹S-2 ¹P, 2 ³S-n³P (n=2, 3) and 2 ^1,3P-n^1,3D (n=3, 4) transitions. The dipole and quadrupole polarizabilities for the ground He (1s²¹S) state are also reported for each screening parameter. Results obtained are useful in plasma diagnostic purposes besides several other applications.     

高氧空位简并锐钛矿TiO2半导体电子寿命的第一性原理研究

为了研究锐钛矿TiO₂晶体中高氧空位浓度对电子寿命的影响,利用基于局域密度泛函理论框架下的广义梯度近似平面波超软赝势方法, 用第一性原理对含高氧空位浓度的锐钛矿TiO₂晶体进行了结构优化处理、能带分布和态密度分布计算, 表明在温度一定和高氧空位浓度的条件下, 锐钛矿TiO₂的电子寿命随氧空位浓度的增大而减小;电子浓度的大小对电子寿命无影响.同时,锐钛矿TiO₂晶体中高氧空位浓度时,发现有莫特相变的现象. 关键词： 高氧空位 2半导体')" href="#">锐钛矿TiO₂半导体 电子寿命 第一性原理     

Pt掺杂CdS光学性质的第一性原理研究

基于密度泛函理论的第一性原理平面波超软赝势方法,运用Castep计算分析了Pt元素掺杂CdS结构,对本征CdS和掺杂晶体的能带结构、态密度以及光学性质进行了分析对比, 由掺杂前后的结果分析发现：Pt掺杂闪锌矿相CdS产生了新的能带,带隙明显缩小;CdS的吸收边产生红移,禁带宽度变窄,在可见光区具有较大吸收系数,提高了可见光的利用率,表现出较好的可见光光催化活性。