Density Functional Theory Study For W_mC_n(m+n≤7) Clusters

In this paper, Gaussian03program based on density functional theory is applied.The geometric structures of W_mC_n（m+n≤7）clusters are all optimized systematically,and the ground state structures are investigated. The main results are as follows:Firstly,The possible equilibrium geometries and stability of W_mC_n（m+n≤7）clusters are optimized by using the density functional theory at the B3LYP/LANL2DZ level. For the ground state structures, the average binding energy （Eb）,second difference in energy（△2E），HOMO-LOMO gaps （Eg） and the Wiberg bondindex（WBI） are analyzed. With the increasing of tungeten atoms, the structures ofclusters transform linear into planar, and then into three-dimensional stucture. Thespin multiplicity is not more than5. The hybridize of Carbon atoms enhanced thestability of the clusters, but reduced the chemical activity. And the Wiberg of W-C ismuch stronger than that of w-w and C-C, so it is easier to form W-C bond in theW_mC_n（m+n≤7） clusters.Secondly, after getting the ground state structures of W_mC_n（m+n≤7）clusters，Thepossible equilibrium geometries and stability of W_mC_n（m+n≤7） clusters are optimizedby using the density functional theory at the B3LYP/LANL2DZ level. For the groundstate structures, vibrational spectrum；NBO are analyzed. The calculation resultsshow that: in the process of W and C atoms in the atomic charge W,6S orbit transferto C2p atomic orbitals, the orbital hybridization phenomenon, the formation of W-Cchemical bond stronger; vibration spectrum analysis showe that: the vibrationfrequency is mainly distributed in the12.22cm-1to2091.22cm-1, peak the maximumfrequency and the corresponding vibration mode for most of the C or W atomstretching vibration.Thirdly，The possible equilibrium geometries and stability of W_mC_n（m+n≤7）clusters are optimized by using the density functional theory at the B3LYP/LANL2DZlevel for the ground state structure of the dipole emoments, polarization rate andmagnetic are optimized, the results show that the W_mC_n（m+n≤7） cluster in additionW₂C₂cluster, W₂C₃cluster are the polarity, WC6cluster total dipole moment is thelargest, the strongest polarity; Cluster polarization rate shows that in XY direction,cluster W_mC_n（m+n≤7） susceptibility tensor component for maximum46.66In XZ direction, clusterW_mC_n（m+n≤7） susceptibility tensor component maximum value is11.38; In the direction of YZ, cluster W_mC_n（m+n≤7） susceptibility tensor componentin addition to W5C cluster for3.06the rest are zero; Hybrid cluster total magneticmoment range in0⁴μB, clusters of magnetic moment are mainly W atomic clustersprovided, in part, there is a "magnetic moment quenching" phenomenon. tensorcomponents to the maximum value of46.66in the XZ direction cluster W_mC_n（m+n≤7） polarizability tensor components of the maximum value is11.38in thedirection of YZ, W_mC_nclusters（m+n≤7） polarizability tensor components except theW5C cluster as the-3.06and the rest are all zero; mixed clusters total magneticmoment in the range of0～4μB, magnetic moments of clusters are mainly W atomsprovide," magnetic quenching " phenomenon occurred in some clusters.To sum up, in this paper we have systematically studiied the physical andchemical properties of the ground state of W_mC_n（m+n≤7） clusters, and revealed theinternal relation between microstructure and macro-properties on clusters. This articlecould provide a reliable theoretical basis for experimental research and an appropriatemodel for developing new functional materials.Above all,it is the first time to study the physical and chemical properties ofground state of the W_mC_n（m+n≤7） clusters, it rveals the macro properties andmicrostructure of W_mC_n（m+n≤7） clusters,and provided the reliable theory of theexperiment,The researches will play an important role in understangding the richtungsten cases of tungsten carbide and finding new function marerials.