NSTI Nanotech 2009

Comparing the Stabilities of Nanoclusters and Cluster-Based Materials: Alkali Halides and the First Row Element Compounds

W. Sangthong, S.T. Bromley, F. Illasc, J. Limtrakul
Kasetsart University, TH

Keywords: nanoporous zeolite sodalite, Alkali halide nanoclusters, density functional theory, nanoporous alkali halide, first principles bottom-up study

Abstract:

The stability of (MX)12 cage clusters and cluster-based polymorphs of a large range of alkali halides and the first row element compounds (LiF, BeO, BN and C) were investigated using state-of-the-art plane wave density functional (DF) calculations. Specifically, a nanoporous analogue of the zeolite sodalite (SOD-MX) can be regarded as being assembled from (MX)12 cluster building blocks. For all alkali halides the dense rs-MX phase was found to be more stable than the low-density nanoporous SOD-MX phase. The energy difference between the rs-MX and the SOD-MX bulk polymorphs (per MX unit) was found to increase with increasing ionic radius ratios with the same anion, but at the highest ionic radius ratio the differences decrease. Correspondingly, the cage-based SOD-LiX phases were all found to be only marginally metastable energetically with respect to the rs-LiX forms (ΔESOD-rs≤0.05 eV/LiX). For the first row element compounds, the energy difference between the ground state phases and the SOD-MX bulk polymorphs (per MX unit) was found to increase when consider from LiF to C (ΔESOD-stab=0.05, 0.17, 0.68, 1.07 eV/unit for LiF, BeO, BN and C, respectively). The results of ELF analysis of (MX)12 cage clusters could be explained the difference of electron distribution on each cluster.
 
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