Co-B非晶态合金中电子转移问题的量子化学研究

根据Co -B非晶态结构的短程有序、Co和B之间是较强的化学作用以及化学键理论 ,设计了ComB2 (m=1～ 4)原子簇模型 ,用DFT方法对其进行高水平的量子化学计算 ,结果表明 ,模型体系ComB2 (m =1～ 4)中 ,B原子供给Co原子电子 ,这与非晶态合金的实验结果一致 ,同时存在B -B直接相连 ,为了比较 ,也选择了ConB (n =1～ 4)模型 ,计算结果与实验不符 ,说明ComB2 (m =1～ 4)原子簇模型更能反映非晶态的结构特点 .

Quantum Chemistry Study of Electron Transfer between B and Co in Co-B Amorphous Alloy

The amorphous alloys are a kind of interesting and promising material in material science. Owing to its special structural character and electronic properties, it provides a path to novel, more active and selective catalysts. Although experimental works on amorphous alloy could be found everywhere, a few theoretical calculations were published in literatures. It does give a challenge to theoretical researcher since it is not easy to model the amorphous structure. Until now, a controversy of the direction of charge-transfer still exists in the study of the Co-B amorphous alloy. According to the experimental results, the charge transfer between Co and B in Co-B amorphous alloy is from B to Co, which seems to be incompatible with the electronegative view in classical chemistry. On the other hand some theoretical calculations showed an opposite conclusion to the experiment. Since many physical and chemical properties like specific heat, magnetic susceptibility, ferromagnetism, superconductivity and catalytic activity are directly related to the electronic properties of the local structure of amorphous alloy, in this case, the charge transfer between Co and B are required to clarify the argument. The previous calculations were, unfortunately, not complete in many aspects; at the very least, the calculated models and methods were too rudimentary. The aim of our present paper is to investigate the electron transfer between B and Co of Co-B amorphous alloy by a series of cluster model ComB2(m=1~4) and Co-B calculations with density functional theory (DFT). Since most of the modeling and simulation concerning amorphous alloy were based on statistical method, which lays emphases on the long-range disordered, they give little information of electronic properties. In order to understand the electronic properties of amorphous alloy in detail, the best way is to calculate it by using a proper model with a correct local structure referring to the experimental fact at the precise level of quantum chemistry calculation. Hence, the present work tries to use a kind of new models. The models are constructed according to the following experimental results: amorphous alloy are packed by small clusters, its local structure is in ordering, and the metal-metalloid is chemically bonded. Our present paper, considering the direct B-B contact in cluster model is the key point that makes our calculations differ from the previous theoretical works. The results of the calculations showed that boron is an electron-donor, while cobalt is an electron-acceptor, which agrees well with the experimental results. It is very possible for Co-B amorphous alloy to exist the direct B-B contact. Compared with the calculation results from another series of ConB(n=1~4) cluster models, It could be concluded that the ComB2(m=1~4 ) clusters is more reasonable for the structure of Co-B amorphous alloy.