A First‐Principles Study on the Electronic, Vibrational, and Thermodynamic Properties of Jadeite and its Tentative Low‐Density Polymorph

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AbstractThe high‐pressure clinopyroxene mineral jadeite (chemical composition NaAlSi2O6) was studied by density‐functional theory with respect to its electronic, vibrational, and thermodynamic properties, correctly reproducing the available experimental data. At a larger‐than‐normal volume, however, a low‐density alumosilicate phase with tetrahedral instead of octahedral Al–O coordination was identified. This low‐density phase was investigated theoretically, too, and the results were compared to jadeite and experimentally observed properties of what has been dubbed jadeite glass. It turned out that the theoretically obtained properties of this hypothetical polymorph, such as the bulk modulus, the molar volume and the vibrational frequencies, agree well with the corresponding properties of the glass phase. Hence, from an inverse structure‐property relationship we propose to model jadeite glass with the aforementioned low‐density alumosilicate phase and tetrahedral Al–O motifs, as suggested from first principles and corroborated from experiment. The possibilities as well as the limitations of electronic, phonon and thermodynamic properties calculations applied to such a polymorph are also discussed.