In this paper, solid-state amorphization induced by mechanical milling is shown to be a useful tool to explore the polymorphism of drugs and their mechanism of devitrification. We show in particular how the recrystallization of amorphous chlorhexidine dihydrochloride obtained by milling reveals a complex polymorphism that involves several polymorphic forms. Two new crystalline forms are identified, one of them appearing as a highly disordered precursor state which however clearly differs from the amorphous one. Several interpretations are here proposed to describe the puzzling nature of this phase. In addition, the possibility to amorphize chlorhexidine dihydrochloride by milling allowed to determine the main physical characters of the amorphous state which cannot be obtained through the usual thermal quench of the liquid because of a strong chemical degradation occurring on melting.

We present a periodic density functional theory investigation of two proton-ordered phases of ice. Their equilibrium lattice parameters,relative stabilities, formation energies, and densities of states have been evaluated. Nine exchange-correlation functionals, representative of the generalized gradient approximation (GGA), global hybrids,range-separated hybrids, meta-GGA, and hybrid meta-GGA families have been taken into account, considering two oxygen basis sets. Although the hydrogen-bond network of ice is well reproduced at the B3LYP,M06-L, or LC- wPBE levels, formation energies are only correctly evaluated with the two former functionals. Band gaps on the other hand are only quantitatively reproduced at the B3LYP level. These results indicate that this last functional, a de facto reference for molecular calculations, gives in average the most accurate results for the considered ice properties.