Excitons in Mg(OH)2 and Ca(OH)2 from ab initio calculations

• Prediction of strongly bond excitons in Mg(OH)2 and Ca(OH)2 by first-principles calculations.
• Many-body effects play a crucial role in the optical absorption spectra of Mg(OH)2 and Ca(OH)2.
• The results have important implications for applications in optoelectronic devices.

By using ab initio calculations with the HSE06 hybrid functional and GW approximation combined with numerical solution of the Bethe Salpeter equation (GW–BSE) we predict the existence of diverse number of excitonic states in multifunctional hydroxides X(OH)2 (X  =Mg and Ca) that were not previously reported experimentally or theoretically. The imaginary part of the dielectric function and the reflectivity spectra show very strong peaks corresponding to the electron–hole pair states of large binding energy. The origin of the excitons is attributed to strong localization of the hole and the electron associated with oxygen 2px,2py2px,2py occupied states as well as to oxygen and earth metal s empty states, respectively. The results have important implications for different applications of the materials in optoelectronic devices.