Abstract
AbstractThe properties of trimer Cs3X3 and tetramer Cs4X4 (X = Br, I) molecules have been studied using DFT with B3LYP5 functional and MP2 and MP4 methods. Two equilibrium geometrical structures of trimers, hexagonal (D3 h) and “butterfly-shaped” (Cs), and one for tetramers, distorted cubic (Td), are confirmed to exist; geometrical parameters and vibrational spectra are determined. The relative concentration of Cs3X3 isomers has been evaluated; the butterfly-shaped isomer dominates over hexagonal in saturated vapour in a broad temperature range. The dissociation reactions through different channels have been considered and enthalpies of formation ΔfH°(0) of clusters determined:−858 ± 20 kJ mol−1 (Cs3Br3), −698 ± 20 kJ mol−1 (Cs3I3), −1270 ± 30 kJ mol−1 (Cs4Br4) and −1045 ± 30 kJ mol−1 (Cs4I4). The Gibbs free energies ∆rG°(T) calculated for the dissociation reactions of trimer and tetramer molecules have indicated that these molecules are resistive in narrow temperature range only and decompose spontaneous...
Highlights
The study of alkali halide clusters, ionic and molecular, has been the subject of research over past five decades
The geometrical parameters and vibrational spectra of these structures are compiled in Tables 1 and 2
For both isomers of Cs3Br3 and Cs3I3, the MP2 method demonstrates higher ionicity as the charge magnitudes are bigger by 0.03–0.07 au than the corresponding values of q obtained by DFT
Summary
The study of alkali halide clusters, ionic and molecular, has been the subject of research over past five decades. On the other hand theoretical studies concern mainly prediction of equilibrium configurations, geometrical parameters, binding energies and vibrational frequencies These clusters are of interest because they have unique electronic, optical and magnetic properties which make them to be useful in different applications. We have theoretically investigated the properties of molecular and ionic clusters of caesium fluoride (Mwanga, Pogrebnaya, & Pogrebnoi, 2015a), caesium chloride (Hishamunda, Girabawe, Pogrebnaya, & Pogrebnoi, 2012; Pogrebnaya, Hishamunda, Girabawe, & Pogrebnoi, 2012) and caesium bromide and iodide (Mwanga, Pogrebnaya, & Pogrebnoi, 2015b) In these works, the equilibrium geometrical structure, vibrational spectra and thermodynamic properties of the clusters were determined. According to Liu, Zhao, Li, and Chen (2013) as well as our previous work (Mwanga et al, 2015a), the DFT methods are not mush sensitive to the BSSE correction and the latter does not improve the DFT results on energies and enthalpies of dissociation reactions
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