We have performed unbiased searches for the global minimum structures of (FeS)n+ (n=1–5) clusters using the CALYPSO method combined with density functional theory geometric optimisation. A large number of low-lying isomers are optimised at the B3PW91/6-311+G* theory level. Accurate ab initio calculations and harmonic vibrational analyses are undertaken to ensure that the optimised geometries are true minimum. They show that the most stable structures begin to exhibit three-dimensional (3D) configurations at n=3. The relative stabilities of (FeS)n+ clusters for the ground-state structures are analysed on the basis of binding energies and HOMO-LUMO gaps. The theoretical results indicate that the binding energies of (FeS)n+ tend to increase with cluster size. The maxima of HOMO-LUMO gaps (3.88 eV) for the most stable configurations appear at (FeS)+. Moreover, we have found that the (FeS)2+ cluster possesses the lowest local magnetic moments compared to the other species. The origin of this magnetic phenomenon is also analysed in detail.
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