【作者】 孔德国；

【导师】 李蕴才；

【作者基本信息】 河南大学 ， 理论物理， 2007， 硕士

【摘要】 本论文首先介绍了计算机分子模拟,以及计算机分子模拟下的材料计算的现状及发展趋势。接着介绍了我们实验室的分子模拟软件(Materiales Studio简称MS),并对该软件进行了说明,以及对本文工作中用到的两个计算模块(CASTEP和Dmol3)的功能和使用进行了简单介绍。接着叙述了凝聚态物理学中传统的单电子近似理论(HFA),以及这一问题的更严格、更精确的描述——单电子近似的近代理论(DFT),以及在这一理论框架下的第一性原理的材料计算方法。结合本实验室的实验工作,选择了本论文研究的材料体系。使用第一性原理计算方法对盆烯分子和锐钛矿型TiO2掺N体系进行了研究。基于密度泛函理论的广义梯度近似(GGA)算法研究了盆烯分子C3nH2n(n是基底碳环上碳原子的个数n=3～12)的几何结构和电子特性,结果表明当n=3~8时可以形成盆形结构,n=9、10时分子变为平面结构,且对称群均为Cnv。n=11、12分子趋于鞍形。此外还研究了它的结合能、能隙、HOMO(Highest occupied molecular orbital)和LUMO(Lowest unoccupied molecular orbital)等,表明这种分子是稳定的,平面结构是这种分子最稳定的构型。且分子的还原能力随着n的增大越来越弱,氧化能力逐渐增强。采用基于第一性原理的超软赝势方法,研究了本征锐钛矿型TiO2和不同量N掺杂所形成的锐钛矿结构的TiO2-xNx合金的电子结构。计算结果表明N的掺杂导致TiO2晶体的禁带宽度减小,发生了红移现象。并且随着N掺入量的不断增加,TiO2-xNx合金的禁带宽度单调减小。研究发现:掺杂前O 2p态电子决定价带顶的位置,且态密度随N的含量的改变发生了稍微的变化。在价带中N 2p态电子比O 2p电子的能量位置要高,掺杂后N 2p态的电子决定价带顶的位置,且随掺杂量的增大N 2p态的高能端向短波方向发生了的移动。Ti 3d态电子决定导带底的位置,并随N的掺入量的增加Ti 3d态的低能端向长波方向发生移动。最终导致了禁带宽度的变窄,发生了红移现象。更多还原

【Abstract】 In this paper, we first introduced computer molecular simulation status and development trend of materials computation with computer molecular simulation. Then molecular simulation software of our laboratory——MS（Materiales Studio）, its instruction and modules used in it（CASTEP and Dmol3）were introduced. Following, we described traditional single electron approximation theory（HFA）in condensed physics and its more precise description——modern single electron approximation theory（DFT）. We described materials computation methods with first-principles based on DFT. Furthermore, we investigated peristylapolyenes and N-doped anatase TiO₂ with this method combined with experimental work of our laboratory.This work investigated geometrical structures and electrical characteristics of C3nH2n molecules with GGA approximate calculation based on DFT（n is the number of carbon atoms of bottom carbon ring ）. The results show that the molecules form basin-structures when n=3～8 and plane-structures when n=9～10 whose symmetry groups are both Cnv. While n=11～12 they form saddle-structures. We also investigated its binding energy, energy gap, HOMO（Highest occupied molecular orbital） and LUMO（Lowest unoccupied molecular orbital）etc, showing that these molecules are stable and plane structures are the most stable form. The results also show that deoxidization capacities become weaker and oxidation capacities become stronger with increase of n.The electronic structures of pure anatase TiO₂ and anatase TiO₂-xNx which can be obtained by different concentrations of N-doping have been investigated by using first-principles ultrasoft- pseudopotential method. The calculation indicates that the band gap of TiO₂ become narrow due to N-doping so-called red-shift. The monotone decrease of band gap of TiO₂-xNx with increasing N concentrations was observed. Our work shows that the top position of the valence band is determined by the O 2p electron state before doping and density of states changed a little with different N-doping. After N doping, top position of the valence band is determined by the N 2p electron state, and it moves to short wavelength with N doping concentration increasing. The bottom position of the conduction band is determined by Ti 3d state, and moves to long wavelength with N doping concentration increasing, leading to narrow energy gap.更多还原