本文選題：第一性原理　切入點(diǎn)：密度泛函理論　出處：《魯東大學(xué)》2017年碩士論文

【摘要】：Fe-B體系,C-N體系超硬材料在力學(xué)性質(zhì)方面具有潛在的應(yīng)用價(jià)值。在過去幾十年中,對于兩種體系的在力學(xué)、磁學(xué)和電學(xué)方面的理論與實(shí)驗(yàn)研究不斷跟進(jìn),但在光學(xué)性質(zhì)方面的研究較少。因此我們利用第一性原理下的多體微擾理論和密度泛函理論方法分別對Fe-B體系和C-N體系的光學(xué)性質(zhì)進(jìn)行研究。利用GGA+PBE方法研究了tP10-FeB4、I41/acd-FeB4和oP12-FeB2三種結(jié)構(gòu)的晶體結(jié)構(gòu)、能帶結(jié)構(gòu)和態(tài)密度等電子結(jié)構(gòu)特征。進(jìn)一步運(yùn)用GW+BSE方法研究分析了其光學(xué)性質(zhì)。結(jié)構(gòu)表明oP12-FeB2能隙小,在吸收系數(shù)上表現(xiàn)為在可見光區(qū)出現(xiàn)明顯的吸收峰,可用作光學(xué)吸收材料;而t P10-FeB4和I41/acd-FeB4由于能隙較寬且在禁帶兩端軌道占據(jù)較少,吸收表現(xiàn)出在紫外吸收較強(qiáng),而在可見光區(qū)吸收非常小。利用密度泛函理論的GGA+PBE方法對C-N體系的十一種結(jié)構(gòu)進(jìn)行了研究。具體分析了晶體結(jié)構(gòu)參數(shù),電子的躍遷機(jī)理,介電函數(shù)峰的成因和光學(xué)性質(zhì)。通過光學(xué)性質(zhì)我們對所有結(jié)構(gòu)進(jìn)行了比較。根據(jù)不同結(jié)構(gòu)的光學(xué)特點(diǎn),加之其本身的力學(xué)特性,我們對這類結(jié)構(gòu)材料的潛在應(yīng)用進(jìn)行了初步的預(yù)測。在C-N體系中選取了I2d-CN2結(jié)構(gòu)進(jìn)行Ti的摻雜研究。通過不同替換方式和調(diào)節(jié)摻雜濃度,分析比較了Ti替換N和Ti替換C元素的結(jié)構(gòu)參數(shù),電子結(jié)構(gòu),光學(xué)性質(zhì)和力學(xué)性質(zhì)。由于外層電子數(shù)不同,Ti替換N產(chǎn)生自旋極化現(xiàn)象,使得光學(xué)性質(zhì)發(fā)生明顯變化。吸收系數(shù)表明,Ti替換N元素在可見光區(qū)吸收較強(qiáng)且在可見光區(qū)吸收明顯強(qiáng)于Ti替換C元素。綜合這些摻雜結(jié)構(gòu)的力學(xué)和光學(xué)性質(zhì),我們確定了獲得兩種最佳性質(zhì)的摻雜濃度。
[Abstract]:The superhard materials of Fe-B system and C-N system have potential application value in mechanical properties.In the past few decades, the theoretical and experimental studies on the mechanical, magnetic and electrical aspects of the two systems have been followed up, but less on the optical properties.Therefore, the optical properties of Fe-B system and C-N system are studied by using the multibody perturbation theory and density functional theory under the first principle, respectively.The structure, band structure and density of state of TP10-FeB _ 4 I41 / acd-FeB _ 4 and oP12-FeB2 have been studied by GGA PBE method.The optical properties are analyzed by GW BSE method.The structure shows that the band gap of oP12-FeB2 is small, and the absorption coefficient appears obvious absorption peak in the visible region, which can be used as optical absorption material, while t P10-FeB4 and I41/acd-FeB4 occupy less orbit at the two ends of the band gap because of the wide gap.The absorption was strong in ultraviolet light, but very small in visible region.Eleven structures of C-N system are studied by using the GGA PBE method of density functional theory.The crystal structure parameters, electron transition mechanism, the origin of dielectric function peak and optical properties are analyzed in detail.All structures are compared by optical properties.Based on the optical characteristics of different structures and their mechanical properties, the potential applications of this kind of structural materials are preliminarily predicted.I2d-CN2 structure was selected to study Ti doping in C-N system.The structural parameters, electronic structure, optical properties and mechanical properties of Ti substitution N and Ti substitution C were analyzed and compared by different substitution methods and doping concentration.The optical properties are obviously changed due to the spin polarization phenomenon caused by the different number of electrons in the outer layer.The absorption coefficient indicates that the absorption of N element in the visible region is stronger than that of the substitution C element in the visible light region.Based on the mechanical and optical properties of these doped structures, we have determined the optimum doping concentrations.
【學(xué)位授予單位】：魯東大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：O469

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