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The Computational Simulation Study on Bulk Moduli of Ⅱ-Ⅲ2-Ⅵ4 Semicoductors

Author: YuanShiMin
Tutor: JiangXiaoShu
School: Shanxi University
Course: Condensed Matter Physics
Keywords: DFT Body modulus Plane wave basis vector Pseudopotential
CLC: O471
Type: Master's thesis
Year: 2010
Downloads: 18
Quote: 0
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Abstract


In the past few decades, based on density functional theory and plane-wave pseudopotential method for first-principles calculations carried out successful multi-body systems research, making first-principles calculations become widely used in quantum computing approximate method. Body modulus is an important mechanical properties of materials, in general body modulus, the more difficult to compress. For Ⅱ - Ⅲ 2 - Ⅵ 4 the body of semiconductor material modulus, essentially no experimental data can be used, so we semiconductor material of the body of the modulus of a computer simulation study. In this paper, we use first-principles calculations of Ⅱ - Ⅲ 2 - Ⅵ 4 bulk semiconductor material modulus for two possible structures (DC Structure and DF structure) are studied. The relationship between energy and volume utilization Birch-Murnghan's equation of state was fitted. Based on this empirical formula extends Cohen. We find from Birch-Murnghan's equation of state bodies obtained modulus, modulus body derivative, DC and DF two structures have similar trends, body modulus and then from S to Se Te, body variable modulus amount gradually decreases, which is mainly due to the bond lengths and different result. For body modulus, we can use the experimental data is not much. Recently, D.Errandonea high pressure X-ray scattering experiments, up to 23GPa the conditions, the structure of the material ZnGa2Se4 changes and phase were studied. They found that in practice there is a defective material structure of the material tin yellow, their high pressure 15.5GPa, while the 18.5GPa in 15.5GPa range, low-pressure and high-pressure phase of the phase coexist, the phase In the case of up to 23GPa remained stable. For a high-pressure phase, they think it belongs to a defective NaCl structure of the material structure. For DFKP structural materials, they get, B0 = 47GPa, B '= 3.9. For a NaCl-type structure of the material, they get, B0 = 50GPa, B '= 4. By extending the calculation made by the body Cohen modulus of the empirical formula, we can calculate the two elements containing sphalerite structure of the material having a bulk modulus material. For a tetrahedral structure of the complex compounds and alloys, we can take the nearest neighbor atoms atomic spacing to extend the empirical formula. Body modulus B of the unit is GPa, nearest neighbor atomic distance d of the unit is A. We note that, in the extended empirical formula, we are only four atoms pitch spacing of three atoms in the summation, which is mainly due to the Ⅱ - Ⅲ 2 - Ⅵ 4 semiconductor material structure of the material, the space instead of a bonded atoms, lead us to only three atomic spacing are summed. However, due Ⅱ - Ⅲ 2 - Ⅵ 4 semiconductor material structure of the material characteristics of the atomic spacing after summation is multiplied by a factor 1/4. As Ⅱ - Ⅲ 2 - Ⅵ 4 semiconductor material composition of the material characteristics of the chemical elements (in a unit cell, comprising four sixth main group elements), we take the value of λ 2. Then from S to Se Te, bulk modulus which gradually decreases, this trend easier for us to understand, in the periodic table, with the value characteristic of weakening, it's modulus in the body decreasing. It can be seen, covalent material characteristics of the material body of a variable modulus greater contribution covalent weakening characteristic, reducing the material modulus of the material body. For the DF and DC structures derived from the empirical formula bulk modulus have similar values. This is mainly due to the electronic structure of these two structures similar to the key length. First-principles calculations with bulk modulus empirical formula for the bulk modulus DF structure, the error is smaller for the DC structure errors. The DF structure, we can use the empirical formula to estimate the volume change modulus values. For DC structure, we should be used with caution empirical formula. These theoretical results are yet to be verified by experiment.

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