Narrow Results

We present a systematic first-principle study of the structures, energetics and electronic structure of (ZnO)_n clusters in the size range 1 ≤ n≤ 12. We show that the planar ring structures are stable for n < 8, while spheroidal structures made out of rings of (ZnO)₃ and (ZnO)₂ are stable for n ≥ 8. We examine the binding energies and HOMO–LUMO gaps of the clusters and try to understand our results from simple physical ideas.

We report the first-principle calculations of ferromagnetism in C-doped ZnO clusters. The carbon impurities in ZnO clusters are doped at substitutional O or Zn sites and at interstitial sites and the total energy calculations suggest C at O site is more stable than that at Zn site. The substitutional C impurity is found more favorable than interstitial C impurity in these clusters. The ZnC region is mainly responsible for the observed ferromagnetism in ZnO:C systems. The average magnetic moment of Zn_nO_n–mC_m clusters is found to be 2 μ_B/C for n, m < 7. For n, m > 6 the magnetic moment decreases below 2 μ_B/C. The magnetic moment in (ZnO)_nC_i; i = 1 – 2 is found to be 0.1–2.0 μ_B/C. The combination of substitutional and interstitial C impurities in ZnO clusters leads to magnetic moment of 0.4–1.0 μ_B/C.

A computational study on adsorption and dissociation mechanisms of H₂ molecule on ZnO cluster was analysed using Density Functional Theory (DFT) approach in Gaussian 09 software. The stable sites for hydrogen adsorption were inferred from the adsorption energy and bond length. Further investigations such as Mulliken charge, HOMO–LUMO energy gap and intrinsic reaction coordinate (IRC) were performed for the stable adsorption sites. It infers that the (ZnO)₆ cluster has the highest binding energy of 1.851eV (O-site) and the least binding energy of $-$3.865eV (O-site), showing most favorable size for both adsorption and dissociation of H₂ molecule. The IRC plot clearly shows the dissociation mechanism of hydrogen on the ZnO cluster.