| 1. |
- Gajewski, Grzegorz, et al.
(författare)
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2D calculation of anharmonic OH vibrations in a layered hydroxide crystal
- 2008
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 129:6, s. 064502-
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Tidskriftsartikel (refereegranskat)abstract
- Anharmonicvibrational frequencies for the Raman-active (A1g) and the IR-active (A2u)modes have been calculated for the LiOH crystal within aplane-wave density functional theory (DFT) framework. We find that atwo-dimensional quantum-mechanical vibrational approach, allowing for anharmonic coupling between symmetricand antisymmetric OH stretching modes, produces OH frequencies—both absolute frequenciesand gas-to-solid frequency shifts—in good agreement with experiment. Remaining errorsin the absolute frequencies are largely a consequence of theDFT model chosen. A one-dimensional normal-mode following vibrational treatment, onthe other hand, fails to reproduce both absolute anharmonic frequenciesand gas-to-solid frequency shifts.
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| 2. |
- Hermansson, Kersti, et al.
(författare)
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Anharmonic OH vibrations in Mg(OH)(2) (brucite) : Two-dimensional calculations and crystal-induced blueshift
- 2009
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 131:24
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Tidskriftsartikel (refereegranskat)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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| 3. |
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| 4. |
- Hermansson, Kersti, et al.
(författare)
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Origin of the OH Vibrational Blue Shift in the LiOH Crystal
- 2008
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society. - 1089-5639 .- 1520-5215. ; 112:51, s. 13487-13494
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Tidskriftsartikel (refereegranskat)abstract
- The O−H vibrational frequency in crystalline hydroxides is either upshifted or downshifted by its crystalline surroundings. In the LiOH crystal, the experimental gas-to-solid O−H frequency upshift (“blue shift”) is approximately +115 cm−1. Here plane-wave DFT calculations for the isotope-isolated LiOH crystal have been performed and we discuss the origin of the OH frequency upshift, and the nature of the OH group and the interlayer interactions. We find that (1) the vibrational frequency upshift originates from interactions within the LiOH layer; this OH upshift is slightly lessened by the interlayer interactions; (2) the interlayer O−H - - - H−O interaction is largely electrostatic in character (but there is no hydrogen bonding); (3) the gas-to-solid vibrational shift for OH in LiOH(s) and its subsystems qualitatively adheres to a parabola-like “frequency vs electric field strength” correlation curve, which has a maximum for a positive electric field, akin to the correlation curve earlier found in the literature for an isolated OH− ion in an electric field.
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| 5. |
- Mitev, Pavlin D., et al.
(författare)
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Anharmonic OH vibrations in brucite: Small pressure-induced redshift in the range 0–22 GPa
- 2009
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Ingår i: American Mineralogist. - : Mineralogical Society of America. - 0003-004X .- 1945-3027. ; 94:11-12, s. 1687-1697
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Tidskriftsartikel (refereegranskat)abstract
- The uncoupled anharmonic OH-stretching vibrational frequency for the layered mineral Mg(OH)2(brucite) has been calculated in the pressure range 0(DFT) calculations were performed, followed by quantum-mechanical vibrational energy calculations.The following findings emerged: (1) The calculated d with the experimental literature value [taken as the average between the Raman and IR-measured slopes for Mg(OH) much smaller than that of traditional H-bond correlation curves in the literature. (3) The main origin of the small d are pressed toward each other. (4) At high pressure, the OH with respect to the variation of the D quadrupole coupling constant is approximately –1 kHz/GPa. −22 GPa. Quantum-mechanical electronic structureν(OH)/dP slope is –4 cm–1/GPa, in agreement2]. (2) The calculated ν(OH) vs. R(O···O) correlation is linear and the slope isν/dP and dν/dR(O···O) slopes is the small electric field variation as the mineral layers− ions show some tendency to be tiltedc axis, and a larger tilt angle leads to a larger ν(OH) downshift. (5) The pressure variation of the D quadrupole coupling constant is approximately –1 kHz/GPa.
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