Ab Initio Investigation of the Micro-species in [CaCl2(H2O)n = 0–12] and Their Raman Spectra
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In this work, the structures of micro-species in [CaCl2(H2O)n = 0–12] were systematically studied by density functional theory. The distances between Ca2+ and the two Cl− ions (rCa–Cl) are all less than 4.2 Å when n = 1–4, which shows that the main species is contact ion pair. When n = 5, the main species is solvent separated ion-pair [CaCl−(H2O)5···Cl−] (SIP/s) with one Cl− dissociated from [CaCl2]. When n = 6–9, the main species is changed into solvent separated ion-pair (SIP/d) with two Cl− dissociated from [CaCl2]. Six water molecules are located in the inner shell and other water molecules hydrate in the outer sphere in the form of hydrogen bonding. When n = 10–12, the main structure is still SIP/d. Moreover, the hydration number of calcium with the most stable structure in the first hydration shell is 7. The inner hydration distance remains almost unchanged and the outer water molecules have little effect on the inner ones. The vibrational frequencies of the water molecules in [CaCl2(H2O) n ] were also studied and discussed in detail.
KeywordsCalcium chloride Density functional theory Solution structure Micro-species Raman spectra
We thank the National Natural Science Foundation of China (Nos. U1607106, 21573268), the Natural Science Foundation of Qinghai (No. 2015-ZJ-930Q) and the instruments and equipment function development technology and innovation project of Chinese Academy of Sciences (2018gl08) for support. We also acknowledge computing resources and time on the supercomputing center of National Super Computing Center in Shenzhen.
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