碱金属在沸石β-笼子中的构型及电子结构和磁性的研究

STUDY ON STRUCTURAL,ELECTRONIC AND MAGNETIC PROPERTIES OF ALKALI DOPED β CAGE

利用第一性的离散变分方法，选取ＬＴＡ型沸石的结构单元β笼子作为模拟ＬＴＡ型沸石的团簇，对β笼子吸附８个和１４个Ｎａ或Ｋ的构型及电子结构进行自洽计算．计算结果表明，吸附的Ｎａ或Ｋ分别吸附在稳定吸附位β笼子的六边形心位附近．由于吸附的Ｎａ或Ｋ之间相距较远（＞０４ｎｍ），它们间的相互作用较弱，没有形成团簇．碱金属Ｎａ或Ｋ的掺入使得在沸石的能隙中出现一些杂质态，这些杂质态的出现可能是导致掺杂体系发光的原因．计算所得到的能隙和低碱金属掺杂ＬＴＡ型沸石光吸收谱的实验结果基本一致．在磁性方面，计算结果表明对吸附８个和１４个Ｎａ或Ｋ情形，计算所得每个Ｎａ及Ｋ的平均磁矩均很小，对吸附８个和１４个Ｎａ情形，所得吸附的Ｎａ的平均磁矩分别为００１μＢ和００２μＢ，β笼子的总磁矩分别为０１０μＢ和０３１μＢ；对吸附８个和１４个Ｋ情形，平均每个吸附的Ｋ的磁矩均为００１μＢ，β笼子的总磁矩分别为０１２μＢ和０２２μＢ。

Abstract The structural and electronic properties of eight and fourteen Na or K atoms adsorbed in the β cage of zeolite LTA(Linde type A) have been studied by using the first principles discrete variational method(DVM)based on the framework of local density formalism.The β cage are used as a cluster to simulate the geometrical structures of alkali metal atoms incorporated into the zeolite cages.It is found that after Na and K atoms are adsorbed by the β cage of zeolite LTA,the adsorbed Na or K cations prefer to stay near the hexagonal center site of the β cage.Since the adsorbed Na or K cations are far away from each other(>0 4nm),the interaction between them is weak and it is hard to say that they form a cluster.The calculated average moment of adsorbed Na or K is very small.For adsorbed eight and fourteen Na,the moments are 0.01μ B and 0.02μ B,respectively and the total moments of the doped β cage are 0.10μ B and 0.31μ B.For adsorbed eight and fourteen K,the moments are all 0.01μ B and the the total moments of the doped β cage are 0.12μ B and 0.22μ B.These results are in agreement with the experimental observation.