Structural, electronic, and vibrational properties of solid Sr(OH)2, calculated with different Hamiltonians

The structural equilibrium parameters, the energetic of formation and hydration processes, and the O–H vibrational frequencies of crystalline Sr(OH)2 have been investigated at the ab initio level using the periodic CRYSTAL package. Both Hartree–Fock (HF) and density functional theory (DFT) Hamiltonians have been used, the latter in its local density (LV), gradient-corrected (PP), and hybrid (B3LYP) versions. The computed Sr(OH)2 structural parameters are in reasonable agreement with experiment, the largest deviation being for the a cell parameter, which is overestimated by all the adopted methods. With respect to experiment, DFT Hamiltonians give errors of the order of 13% for the formation energies, whereas errors for the heats of hydration from the corresponding oxide are as large as 27% for the LV functional. Two families of OH groups occur in the structure, in which one acts as a weak hydrogen bond donor. The fundamental ω01(OH) stretching frequency has been computed for the two OH groups, and their difference compared to experiment is (i) severely overestimated by HF, (ii) underestimated by both LV and PP, and (iii) in fair agreement at the B3LYP level. As a function of the adopted method, good correlation exists between ω01(OH) and (i) the OH equilibrium bond length, (ii) the OH⋯O H bond angle, and (iii) the value of the electric field gradient calculated at the H nucleus. Among the adopted functionals, B3LYP performs best for all considered features, particularly so for the OH vibrational data.