Structural and spectroscopic aspects of SCN^(-)(H₂O)_n clusters and the temperature dependency of the isomers: a parallel tempering based approach

In this work, parallel tempering has been used to explore the quantum chemical surface of SCN$(-)$(H${}_2$O)${}_n$ system for n=1−8. The stretching frequencies and more specifically the shifts in –O–H stretching frequencies in this type of systems can serve as the fingerprint of a particular geometry. That is why, stretching frequencies of the water molecules have been evaluated and the changes in their values with successive addition of water molecules are also observed. The general trend of getting more and more red shifted peaks is also seen. Although, in some cases, the trend is slightly deviated, which is also mentioned and logical explanations have been given. Using this strategy several number of local structures along with the global one can also be located, as in a real experimental scenario, where finite temperature is present, any of the observable properties should not be guided by only the global minimum but should be an averaged out value contributed by the local structures along with the global one for a particular size of the cluster. Keeping this important fact in mind, the conformational populations of different isomers for a particular size have also been investigated for temperatures upto 300 K at 1 atm. pressure.