The plane-wave pseudopotential method using the generalized gradient approximation within the framework of density functional theory is applied to anaylse the bulk modulus, thermal expansion coefficient and heat capacity of LaB6. The quasi-harmonic Debye model, using a set of total energy versus volume obtained with the plane-wave pseudopotential method, is applied to the study of the thermal properties and vibrational effects. We analyse the bulk modulus of LaB6 up to 1500 K. The elastic properties calculations show that our system is mechanically stable. For the heat capacity and the thermal expansion, significant differences in properties are observed above 300K. The calculated zero pressure bulk modulus is in good agreement with the experimental data. Moreover, the Debye temperatures are determined from the non-equilibrium Gibbs functions and compared to available data.
The plane-wave pseudopotential method using the generalized gradient approximation within the framework of density functional theory is applied to analyse the lattice parameters, elastic constants, bulk moduli, shear moduli and Young's moduli of WSi2. The quasi-harmonic Debye model, using a set of total energy versus cell volume obtained with the plane-wave pseudopotential method, is applied to the study of the elastic properties and vibrational effects. The athermal elastic constants of WSi2 are calculated as a function of pressure up to 35 GPa. The relationship between bulk modulus and temperature up to 1200 K is also obtained. Moreover, the Debye temperature is determined from the non-equilibrium Gibbs function. The calculated results are in good agreement with the experimental data.
The present work is devoted to the study of the excitation of two kinds of Si2O isomers. The results show that the is excitation energies, oscillator strengths, transition electric dipole moments and absorption spectra are affected evidently by external electric field. The triangular Si2O(C2v,1A1) has no visible light absorption spectrum under no external electric field, however, it has faint absorption spectrum(407.18—526.93 nm) in the visible region under external electric field. The linear Si-Si-O(C∞v,3Σ-) has absorption spectra in blue light region and in purple light both in the presence and in the absence of external electric field. One of the important results is that the linear Si-Si-O has strong blue light absorption spectrum(478.88—488.59 nm).
Pseudo-potential investigations of structural, elastic and thermal properties of tungsten disilicide * Xu Guo-Liang(徐国亮) a) † , Chen Jing-Dong(陈敬东) b) , Xia Yao-Zheng(夏要争) a) , and Liu Xue-Feng(刘雪峰) a)
The present paper is devoted to the calculating of transition wavelengths, oscillator strength, Einstein An0 and B0ncoefficients of titanium monoxide molecule from ground state to the first six different excited states by employing the density function theory BLYP and the single substitute configuration interaction approach with basis set 6-311 + + G **. The excited states of titanium monoxide molecule under different external electric fields are also investigated. It is shown that the α HOMO-LUMO gaps become smaller and the electrons of the occupied orbital tend to the virtual orbital as the external electric field intensity increases, and the β HOMO-LOMO gaps become bigger, while the variation in excitation wavelength of high-excited states turns more complicated than that of low-excited states, and the coupling strengths of excited states increase with external electric field increasing.
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