Materials properties of magnesium and calcium hydroxides from first-principles calculations

Abstract

This work presents a study of ground state properties, electronic structure, dielectric and optical properties of magnesium and calcium hydroxides X(OH)2 (X = Mg and Ca) within PBE-GGA and range-separated hybrid functional schemes as well as by using GW approximation. The relevant HSE06 hybrid functional mixing parameters were determined from a self-consistent adjustment to the electronic dielectric constant ǫ∞. It was shown that the overall performance of our adaptation of the HSE06 functional via implementation of the modified amount of the Fock exchange is nearly best for the ground state properties as compared to other relevant HF and DFT methods. Structural stability of the crystalline X(OH)2 hydroxides has been considered in static and dynamic aspects. The most important factors describing the bonding situation have been investigated, and a crystalchemical integrity of the hydroxides has been analyzed. From electronic structure studies it was found that both materials are direct band gap insulators. Predictions for the fundamental band gaps were shown to be in the range of 7.7-8.3 eV for Mg(OH) 2 and 7.3-7.6 eV for Ca(OH) 2 . The origin of the conduction and valence band states near the band edges has been studied in terms of orbital and site projected density of states as well as by comparison with the X-ray photoelectron spectroscopy measurements. It was shown that effective masses of carriers at the Γ-point in vicinity of the band extreme are strongly anisotropic and for the electrons are similar to those in the ZnO crystal. Optical properties of the bulk X(OH)2 hydroxides have been investigated in terms of the real and imaginary parts of the optical dielectric function calculated in GW approximation. Electronic character of anisotropy of optical properties has been clarified. On the base of the obtained results the potential of applicability of the Mg(OH) 2 and Ca(OH) 2 crystalline hydroxides in semiconductor device engineering and optoelectronics has been analyzed.

Portlandite crystal: Bulk, bilayer, and monolayer structures

“…Our results are consistent with Ref. [23] and together they have good agreement with experiments. This justifies the reliability of our calculations.…”

“…Although the structural and electronic properties of bulk AEMHs have been investigated before [21,23,24], single layers of these materials have never been studied before and the their stability is still an open question. However, advances in experimental techniques made exfoliation and growth of such structures possible [25,26].…”

Two Faces of Hydrogen in Yttrium Hydroxyhydride: Y2H3O(OH) – a New Inorganic Chiral System with Hydridic and Protonic Hydrogens

“…In contrast, the O(2) atom puts together the H(4) site, occupied by proton, and the metal center. Such arrangement is a typical feature of hydroxides 27 which is necessary for fixation of H + in the crystal lattice. The final stabilization of H + proceeds then via the ion pairing effect which results in the formation of the (OH)anion.…”

Surface Properties of Metal Hydroxide Microparticles in the Ambient Air

“…In a number of conversions that occur under tropospheric conditions (СаО → Са(ОН) 2 → СаСО 3 ), the band gap of these compounds varies from 7.03 eV (calcium oxide) [6] to 7.3 ÷ 7.6 eV (calcium hydroxide) [7] and 5.0 eV (calcium carbonate) [8]. Due to high water vapor content (as compared to carbon dioxide), calcium oxide is converted to calcium hydroxide with the absorption spectrum shown in Fig.1 (curve 1).…”