钠硼硅玻璃形成体II的第一性原理研究：玻璃态
First principles study of a sodium borosilicate glass-former II: The glass state
摘要：
采用从头算方法研究了3 Na_2 O-B_2 O_3-6SiO_2钠硼硅玻璃的性质。我们发现，径向分布函数g_BO（r）和g_BNa（r）的第一个峰的加宽是由于三角形和四面体硼单元的存在以及与BO_3单元相连的非桥氧原子的存在。与实验结果一致，我们发现[3]B单元涉及大量的非桥氧，而绝大多数[4]B只有桥氧。我们确定了[3]B和[4]B单元周围Na原子的三维分布，并利用这些信息解释了为什么与后者相关的钠原子与中心硼原子共享的氧原子比前者多。从电子的分布，我们计算总的电子态密度，以及它的分解成角动量的贡献。振动态密度在高频率处显示出源自硼原子运动的带。此外，我们表明，[3]B和[4]B单元在光谱中产生了明确的特征，因此可以用来估计这些结构实体的浓度。[3]B的贡献可以进一步分解为对称和非对称部分，这些部分也可以在光谱中容易地识别。我们表明，在光谱中的某些功能，可以用来获得信息的类型的原子，是第二个最近的邻居的硼在[4]B单元。我们计算的平均玻恩电荷的桥接和非桥接氧原子，并表明，这些线性依赖于两个键之间的角度和距离连接的阳离子，分别。最后，我们计算了介电函数的频率依赖性以及吸收光谱。
英文摘要：
We use ab initio simulations to investigate the properties of a sodium borosilicate glass of composition 3Na_2O-B_2O_3-6SiO_2. We find that the broadening of the first peak in the radial distribution functions g_BO(r) and g_BNa(r) is due to the presence of trigonal and tetrahedral boron units as well as to non-bridging oxygen atoms connected to BO_3 units. In agreement with experimental results we find that the [3]B units involve a significant number of non-bridging oxygens whereas the vast majority of [4]B have only bridging oxygens. We determine the three dimensional distribution of the Na atoms around the [3]B and [4]B units and use this information to explain why the sodium atoms associated to the latter share more oxygen atoms with the central boron atoms than the former units. From the distribution of the electrons we calculate the total electronic density of states as well its decomposition into angular momentum contributions. The vibrational density of states shows at high frequencies a band that originates from the motion of the boron atoms. Furthermore we show that the [3]B and [4]B units give rise to well defined features in the spectrum which thus can be used to estimate the concentration of these structural entities. The contribution of [3]B can be decomposed further into symmetric and asymmetric parts that can also be easily identified in the spectrum. We show that certain features in the spectrum can be used to obtain information on the type of atom that is the second nearest neighbor of a boron in the [4]B unit. We calculate the average Born charges on the bridging and non-bridging oxygen atoms and show that these depend linearly on the angle between the two bonds and the distance from the connected cation, respectively. Finally we have calculated the frequency dependence of the dielectric function as well as the absorption spectra.
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