  By using \textit{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 \ce{\textit{X}(OH)2} (\textit{X}= Mg and
Ca) that were not previously reported experimentally or theoretically.
Imaginary part of the dielectric function and 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 electron associated to oxygen $2p_x, 2p_y$ 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.
