2D calculation of anharmonic OH vibrations in a layered hydroxide crystal.

Anharmonic vibrational frequencies for the Raman-active (A1g) and the IR-active (A2u) modes have been calculated for the LiOH crystal within a plane-wave density functional theory (DFT) framework. We find that a two-dimensional quantum-mechanical vibrational approach, allowing for anharmonic coupling between symmetric and antisymmetric OH stretching modes, produces OH frequencies—both absolute frequencies and gas-to-solid frequency shifts—in good agreement with experiment. Remaining errors in the absolute frequencies are largely a consequence of the DFT model chosen. A one-dimensional normal-mode following vibrational treatment, on the other hand, fails to reproduce both absolute anharmonic frequencies and gas-to-solid frequency shifts. [ABSTRACT FROM AUTHOR]