Electron Density Distribution of Hydrogen in Solids Obtained by the Maximum Entropy Method

这项科学研究旨在从实验上研究氢在固体中的精确电子密度分布。为此，作为研究的一部分，开发了一种名为最大熵方法(MEM)的新方法。为了建立该方法，利用MEM对粉末X射线衍射数据进行了分析，得到了不同材料的电子密度分布。研究发现，MEM是将精确测量的X射线衍射数据以电子密度的形式可视化的一种非常有效的方法。对于氢在固体中的电子密度，发现在氢键的情况下，电子密度更接近共价键电子的分布，而在非氢键的情况下，电子的密度分布是非常球形的。球状分布的离子电荷与氢的负离子相对应。在这两种情况下，假定固体中氢的电子分布为自由原子是不合适的。似乎没有理由在最小二乘精化中使用氢的原子形状因子。这增加了用X射线衍射法在固体中寻找氢的难度。最大熵方法将在未来的许多材料中观测到氢的精确电子密度分布。

This scientific research aimed to investigate experimentally the pre- cise electron density distribution of hydrogen in solies. For that purpose, a new method called the Maximum Entropy Method (MEM) was developed as a part of the research. In order to establish the method, electron density distributions of various materials were obtained by applying MEM to powder X-ray diffraction data. It was found that MEM was very powerful method to visualize the accurately measured X-ray diffraction data in the form of electron densities. As for electron densities of hydrogen in solids, it was revealed that electron densities in the case of hydrogen bond distributed more like covalent bond electrons, whereas very spherical density distribu- tion of electrons were observed in the case of non-hydrogen bonding. The ionic charge of spherical distribution was found to correspond to negative ion of hydrogen. In both cases, it not appropriate to assume the distribu- tion of electrons of hydrogen in solids as a free atom. It seems that there is no justification to use the atomic form factor of hydrogen in the least squares refinement. This increases the difficulties to find the hydrogen in solids by X-ray diffraction. The precise electron density distribution of hydrogen will be observed by the Maximum Entropy Method in many materials in future.