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采用遗传算法(Genetic algorithm,GA)对B-Al二元团簇[B_xAl_(13-x)]~-(x=0～13)进行了全局结构搜索,并在密度泛函理论(Density Functional Theory,DFT)下对其进行了优化计算.结果表明在二元团簇中,随着硼原子的数量逐渐增加,团簇的结构由二十面体(3D)逐渐转化为准平面(2D)且团簇结构由B与Al原子的比例所决定的.当x=0~7时,Al原子占多数,团簇保持3D结构;反之团簇呈现2D构型;在x=7~8时,团簇的结构发生由3D向2D的转变.能量决定着团簇的稳定性(例如相对能量).能量越小,其结构越稳定.在计算相对能量Erel,当x=1时,其相对能量最低,团簇结构最稳定.为了进一步了解团簇的稳定性,计算了[BxAl13-x]-团簇的HOMO-LUMO能级差(EH-L)和垂直电离能(Vertical Detachment Energies,VDE),并且发现它们的值在整体上是随着B原子数量的增加而减小,表明其团簇的稳定性逐渐减弱.在所有的团簇中,BAl_(12)~-的能级差最大,结构最稳定.因此文章中对其进行了分子轨道分析,发现当一个B原子替代了Al_(13)~-团簇中的中心Al原子时,所得到的BAl_(12)~-的电子壳层结构的1s~2和1p~6几乎和Al_(13)~-团簇保持一致.此外,对于x=13时的准平面全硼团簇B_(13)~-,文章中用适应性自然密度划分(Adaptive Natural Density Partitioning,Ad NDP)对其化学成键进行了分析,结果显示B_(13)~-有8个π电子,具有π反芳香性.
The global structure of B-Al binary clusters [B_xAl_ (13-x)] ~ (x = 0 ~ 13) was investigated by genetic algorithm (GA). The density functional theory , DFT). The results show that with the increase of the number of boron atoms in the binary cluster, the structure of the cluster gradually changes from icosahedral (3D) to quasi-planar (2D) The cluster structure is determined by the ratio of B to Al atoms. When x = 0 ~ 7, the Al atoms occupy the majority, and the clusters maintain the 3D structure; on the contrary, the clusters exhibit 2D configurations; at x = 7 ~ 8, Structure changes from 3D to 2D. The energy determines the stability of the cluster (eg, relative energy). The smaller the energy is, the more stable its structure. When calculating the relative energy Erel, the relative energy is the lowest when x = 1, The cluster structure is the most stable.In order to further understand the stability of the clusters, the HOMO-LUMO energy levels (EH-L) and vertical ionization energies (VDE) of [BxAl13-x] Their values decrease with the increase of the number of B atoms, which indicates that the stability of their clusters gradually diminishes. Among all the clusters, BAl_ (12) ~ - Therefore, molecular orbital analysis is carried out in this paper and it is found that when a B atom replaces the central Al atom in the Al_ (13) ~ - cluster, the resulting electron shell structure of BAl_ (12) ~ - 1s ~ 2 and 1p ~ 6 are almost the same as those of Al_ (13) ~ - clusters.In addition, for the quasi-planar boron clusters B_ (13) ~ ~ AdNDP) was used to analyze the chemical bonding. The results showed that B_ (13) ~ - has 8 π-electrons and has π anti-aromaticity.