Vibration analysis of O-H stretching mode in Mg(OH)2, Ca(OH)2, LiOH, and NaOH by plane-wave pseudopotential DFT calculation

The performance of O-H vibration analysis using a potential energy curve evaluated using plane-wave pseudopotential DFT calculation was studied for several metal hydroxides. The structural parameters, hydration energy, and interlayer energy were also evaluated. Generalized gradient approximation (GGA) yielded superior results to those of local density approximation (LDA) in most evaluations, although even GGA was prone to underestimate the O-H fundamental frequency of the Raman-active mode to a considerable degree. The calculated O-H frequency depended not only on the functional, but also on the pseudopotential and the basis set. Comparison with the calculated O-H frequency of free OH− ion in a vacuum enabled the estimation and correction of the influence of the pseudopotential on the O-H frequency. By applying this correction, the difference of fundamental frequencies between experimental values and values calculated with GGA functionals was less than 90 cm−1.