A Density Functional Theory Study For W_n C^0,± (n=1-6) Clusters

It is known to us that cluster is a basic constitutional unit of nanomaterials whose properties could be designed by controlling the size, geometry structures and compositions. Therefore, it is an important step to study the ground state structures,stablility and electronic properties of cluster for designing micro structures of a new nanomaterial with prescribed properties. In this article, we have applied density functional theory (B3LYP method) to study W_nC^0,±(n=1～6)clusters at Lanl2dz level,the results are as follow:Firstly, The possible equilibrium geometries of W_nC^0,±(n=1～6)clusters are optimized ,and the ground state structures obtained. The calculated results show that: The ground state structure of neutral,anionic and cationic are similar at the same size,and most ground state structure have low spins which is similar with pure Wn clusters ; When n>3, the clusters undergo a transition from two-dimensional structure to three-dimensional structure, and the carbon atom remains on the surface of clusters. Through the average binding-energy and second-order difference of energy analysis, the stability of Wn cluster is increased alone with doped carbon atom. Moreover W₃C is the most stable of W_nC^0,±(n=1～6)clusters, so that it takes as the basic structure.After getting the ground state structures of W_nC^0,±(n=1-6) clusters, we carefully analysis various properties of them at the B3LYP/LANL2DZ level. For examples, through natural bonding orbital (NBO) analyzed the electronic distribution and interaction mechanism between W atom and C atom; compared the ability of gain and lose electronic with the pure Wn clusters; in magnetic aspects, electronic spin density figures and the energy level of frontier molecular orbital were used to show the main magnetic origin of W₂C^0,± and W₄C^0,±clusters; analyzed the infrared vibration features and relevant vibration modes , the red-shift and blue-shift were also explained and exhibited the response of external electric field by analyzing polarizability.Above all, it is the first time to study the physical and chemical properties of the ground state of W_nC^0,±(n=1-6) clusters. All of these cluster researches will play an important role in understanding the rich tungsten cases of tungsten carbide and finding new functional materials.