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Published on: January 16, 2017
Anharmonic OH vibrations in Mg(OH)2 (brucite): two-dimensional calculations and crystal-induced blueshift
Kersti Hermansson1, Michael M Probst, Grzegorz Gajewski
1Materials Chemistry, The Angstrom Laboratory, Uppsala University, Box 538, 75121 Uppsala, Sweden. kersti@mkem.uu.se
Abstract:
A two-dimensional quantum-mechanical vibrational model has been used to calculate the anharmonic OH vibrational frequencies in the layered Mg(OH)(2) (brucite) crystal. The underlying potential energy surface was generated by density functional theory (DFT) calculations. The resulting OH frequencies are upshifted (blueshifted) by about +75 cm(-1) with respect to the gas-phase OH frequency (+120 cm(-1) in experiments; the discrepancy is mainly due to inadequacies in the DFT and pseudopotential models). The Raman-IR split is about 50 cm(-1), both in the calculations and in experiments. We find that the blueshift phenomenon in brucite can qualitatively be explained by a parabolalike "OH frequency versus electric field" correlation curve pertaining to an OH(-) ion exposed to an electric field. We also find that it is primarily the neighbors within the Mg(OH)(2) layer that induce the blueshift while the interlayer interaction gives a smaller (and redshifting) contribution.
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