锂碳掺杂团簇的结构稳定性及Eu/N共掺杂Ti02光学性质的第一性原理研究

【作者】 刘芳；

【导师】 姜振益；

【作者基本信息】 西北大学 ， 凝聚态物理， 2015， 博士

【摘要】 纳米团簇作为构成物质的原子分子和凝聚态物体之间的中间态,研究它的结构及性质有助于更好的理解原子分子等微观粒子及凝聚态固体等的结构及性质。而且它在表面科学、材料科学甚至核物理、天体物理、大气物理中部有所应用。对团簇的结构稳定性及其性质的研究成为开发新型材料的理论技术基础。碱金属锂及其掺杂团簇作为一种功能特殊的新型材料,因其在燃烧、催化、晶体生长、成核、凝固、相变、光学等方面的广泛应用,成为科学家们关注的重点。它的结构稳定性及光学性质的研究,更显得尤为重要。本文主要是基于第一性原理的密度泛函理论,运用GAUSSIAN软件包,考虑了电子关联与交换能,采用B3LYP方法,6-31G(d)基组对碱金属锂团簇Lin+/0/-(n=2-10)及非金属碳元素掺杂锂团簇LinC+/0/-(n=1-8)体系作了模拟计算,对其基态结构、稳定性、电子性质及振动光谱等性质作了分析研究。用VASP程序对非金属元素Eu/N掺杂TiO2光催化材料的光学性质作了研究。得到的主要结果如下：(1)Lin+/0/-团簇的基态结构形成、电子性质及振动光谱都随着团簇所含原子数目的增加而变化。对于基态结构而言,在n<6,原子数目增加时,Lin+/0/-团簇的结构可以看成是在Lin-1+/0/-团簇基态结构不同位置增加一个锂原子得到,当n≥6时,原子数目增加,团簇结构更密集。团簇的离解能及二阶能量离差表明Li2,Li4,Li8,Li3+/-团簇稳定性较好。团簇的振动光谱分析结果表明团簇的光谱靠近指纹区域,奇特的是,通过计算最高振动频率与最低振动频率之差,发现除Li9团簇外,Li。基态结构的频率差奇偶振荡状。Lin-随着原子数目的增加,团簇的振动光谱背离指纹区域。+/0/-团簇基态结构、电子性质及振动光谱都随着团簇所含原子数目的增加而变化。对LinC+/0/-团簇的基态结构来说,除Li2C+和Li6C-外,其它的都具有较好的对称性且处于低电子态,但离子团簇的对称性要低于其中性团簇基态结构。中性团簇的第-个立体结构的团簇是Li4C而离子团簇的第一个立体结构的团簇是Li3C+/-。LinC+/0/-团簇的二阶能量离差及最高占据轨道与最低未占据轨道的能隙表现出奇偶振荡的特点,除Li5C+/-外,n为偶数的团簇比相邻的n为奇数团簇更稳定。团簇的振动频率分析表明它的振动光谱全部落入指纹区域。奇特的是,当锂原子数为偶数时,基态结构的频率差是最小的,相反当锂原子数为奇数时,基态结构的频率差却是最大的。(3)利用平面波方法对Eu/N分别掺杂及共掺杂锐钛矿TiO2体系的电子结构和光催化性质进行了计算。Eu/N共掺杂比单掺杂TiO2更容易掺到晶体中去,而且Eu和N原子易替位的都是Ti原子。对Eu/N掺杂锐钛矿TiO2,使得禁带宽度变窄,导致吸收光谱边缘发生红移现象,最终导致体系的光催化活性增强。Eu掺杂TiO2体系,光吸收能力没有增强。N掺入TiO2可见光吸收能力增强。Eu/N共掺杂锐钛矿TiO2体系,由于Eu和N杂质的协同效应,体系对可见光的吸收能力增强,同时具有很强的可见光光催化活性。更多还原

【Abstract】 Nano clusters as an intermediate state of microscopic particles and condensed matter, studying on its structure and nature helps understanding that of microscopic particles and the structure and properties of condensed matte. And it was applied in surface science, materials science, andeVen in nuclear physics, astrophysics. The study of stability of structure and properties of clusters become theoretical basis in developing new materials. Alkali metal lithium cluster and doping clusters are becoming a focus for sciestists because its wide application in combustion, catalytic, crystal growth and nucleation, coagulation and phase transformation, optical, etc. espcically for its structural stability and optical properties.Based on the first principles density functional theory, using GAUSSIAN packages, we taking the electron correlation energy and exchange energy into account, using B3LYP method and 6-31 g (d) basis set, making simulation calculation for the alkali metal lithium clusters Lin+/0/- (n=2-10) and non-metallic carbon doped lithium clusters LinC+/0/- (n=1-8) system.The ground state structure, stability, and electronic properties and vibration spectrum properties were analyzed. We also made Eu/N doping TiO2 photocatalysis on the optical properties using Vasp package. The main results are shown as follows:(1) The ground state structure, electronic properties and vibration spectrum of Lin+/0/-clusters are changed with the increase of the number of Li atoms. For the ground state structure, we can get Lin+/0/- by adding a lithium atom to Lin-i+/0/- when n< 6, the ground state structure of Lin+/0- become more dense with the increasing of the number of Li.The dissociation energy and second-order energy dispersion of Lin+/0/- shows Li2, Li4, Li8, Li3+ clusters has good stability. The vibration frenqency shows that the vibration spectrum located near to fingerprint area. It is magic that the difference between the maximum vibration frequency and the minimum vibration frequency of the ground state structure shows odd-even oscillation except for Li9. The Lin- vibration spectrum was deviated from the fingerprint area.(2) The ground state structures, electronic properties and vibration spectrum of LinC+/0/-clusters are changed with the increase of the number of Li atoms. For the ground state structure, LinC+/0/- clusters has the high symmetry and low electronic state except Li2C+ and Li6C-, but the symmetry of LinC+/- clusters is lower than that of LinC. The first three-dimensional structure of LinC is Li4C while that of LinC+/- is Li3C+/-. The second order dispersion and the HOMO-LUMO (Egap) of LinC+/0/- clusters show odd-even oscillation. And n-even number of clusters is more stable than the adjacent n-odd number clusters except LisC+/-. The vibration frequency shows the vibration spectrum all located in the fingerprint area. It is Strange that the ground state of the structure of the frequency difference is the smallest when the lithium atoms iseVen, on the contrary when the number of lithium atom is odd number, the structure of the ground state of the frequency difference is the biggest of all.(3)We calculated the electronic structure and optical properties of Eu/N doping TiO2 system using the plane wave pseudopptetial approach accouting spin polarization. The Eu/N doping is easier than single Eu or N doped TiO2 crystals, and the Ti atom is replaced by Eu and N atom. The forbidden band width gets narrow by Eu/N doping anatase TiO2. This leads to margin of absorption spectrum redshift, ventually enhanced photocatalytic activity. The Eu doped TiO2 system doesn’t enhance its capability of light absorption. N doped TiO2 makes visible light absorption ability enhancement. The Eu/N doping TiO2 system makes the absorption ability of visible light and the visible light catalytic activity enhanced.更多还原