Density Functional Theory Study For W_nNi_m(n+m=8) Clusters

In this paper, Gaussian03program based on density functional theory is applied. Thegeometric structures of WnNim（n+m=8） clusters are all optimized systematically, and theground state structures are investigated. The main results are as follows:Firstly, the possible equilibrium geometries of WnNim（n+m=8） clusters are optimizedby using the density functional theory at the B3LYP/LANL2DZ level. For the ground statestructures, the average binding energies, WBI, magnetism and NBO are analyzed. Thecalculated results show that: with the increase of the W atom, the cluster becomes morestable. The strength of order in WBI is W-W＞W-Ni＞Ni-Ni. When n≥5, theWnNim（n+m=8） clusters include the basic structure of Wn cluster. The magnetic moment ofWnNim（n+m=8） clusters is quenched at n=5and6. In the interior of W, Ni atoms, thehybrid phenomenon happens owing to the charge transfer. And the charge transfer alsooccurs between W and Ni atoms so that the interaction of W and Ni transform into thestrong chemical bond.Secondly, after getting the ground state structures of WnNim（n+m=8） clusters, thedipole moment, polarizability and vibrational spectrum are analyzed carefully at theB3LYP/LANL2DZ level. We find that all the clusters of WnNim （n+m=8） have polarity,and rich W clusters, which nonlinear optical effect is strong, are easy to be polarized byexternal electromagnetic field; Vibrational frequency is mainly distributed in0-350cm-1range, but the cluster of W₄Ni₄, with the particularity of vibration mode, has obviouslystrong peak on IR spectrum and Raman spectrum in the frequency of421.971cm-1; TheW₅Ni₃cluster, with high symmetry of C3vpoint group, appear resonance phenomenon on IRspectrum; In the same cluster, the frequency value of stretching vibration between W-atomsis higher than rocking vibration between Ni-atoms.Thirdly, molecular orbital energy level, HOMO orbital level, LUMO orbital level,aromatic properties and thermodynamic properties are analyzed carefully at theB3LYP/LANL2DZ level. The calculated results show that: W₂Ni₆cluster, with low energygap, has strong chemical activity, and its component for frontier orbital are basically thesame, while W₆Ni₂cluster, with high energy gap, has weak chemical activity. The molecularorbit between Alpha and Beta in cluster W₅Ni₃and W₆Ni₂are complete degenerate, and allthe electronic is strictly paired off. The clusters of W₁Ni₇, W₅Ni₃, W₆Ni₂, W₇Ni₁have aromaticity, while W₂Ni₆cluster has antiaromaticity; The enthalpy of formation for all theclusters WnNim（n+m=8） are negative, so it is stable on thermodynamics; Chemicalproperties of the W₂Ni₆、W₃Ni₅、W4Ni4、W7Ni1clusters are mainly dependent on theelectronic in5d-orbit of W atoms.To sum up, in this paper we have systematically studiied the physical and chemicalproperties of the ground state of WnNim（n+m=8） clusters, and revealed the internal relationbetween microstructure and macro-properties on clusters. This article could provide areliable theoretical basis for experimental research and an appropriate model for developingnew functional materials.