High-pressure structural, elastic, and electronic properties of the scintillator host material<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi mathvariant="normal">K</mml:mi><mml:mi mathvariant="normal">Mg</mml:mi><mml:msub><mml:mi mathvariant="normal">F</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>

The high-pressure structural behavior of the fluoroperovskite $\mathrm{K}\mathrm{Mg}{\mathrm{F}}_{3}$ is investigated by theory and experiment. Density functional calculations were performed within the local density approximation and the generalized gradient approximation for exchange and correlation effects, as implemented within the full-potential linear muffin-tin orbital method. In situ high-pressure powder x-ray diffraction experiments were performed up to a maximum pressure of $40\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ using synchrotron radiation. We find that the cubic $Pm\overline{3}m$ crystal symmetry persists throughout the pressure range studied. The calculated ground state properties---the equilibrium lattice constant, bulk modulus, and elastic constants---are in good agreement with experimental results. By analyzing the ratio between the bulk and shear moduli, we conclude that $\mathrm{K}\mathrm{Mg}{\mathrm{F}}_{3}$ is brittle in nature. Under ambient conditions, $\mathrm{K}\mathrm{Mg}{\mathrm{F}}_{3}$ is found to be an indirect gap insulator, with the gap increasing under pressure.

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