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Anharmonic contribution to the stabilization of Mg(OH)2 from first principles
P Treviño1, A C Garcia-Castro, S López-Moreno
1Centro de Investigación y Estudios Avanzados del IPN, MX-76230, Querétaro, Mexico. polivia@cinvestav.mx.
Physical Chemistry Chemical Physics : PCCP
|June 21, 2018
Summary
Density functional theory reveals magnesium hydroxide
Area of Science:
- Materials Science
- Computational Chemistry
- Solid State Physics
Background:
- Magnesium hydroxide (Mg(OH)2) research is extensive, particularly for the P3[combining macron]m1 phase.
- Debate persists regarding the ground state crystal structure and the influence of OH vibrations on Mg(OH)2 stabilization.
- Precise hydrogen positions in Mg(OH)2 are undefined, impacting crystal symmetry, vibrational properties, and thermal stability.
Purpose of the Study:
- To investigate the stability of proposed magnesium hydroxide crystal structures.
- To clarify the role of hydrogen positions in Mg(OH)2 polymorphism.
- To determine the most stable Mg(OH)2 phase under varying temperatures.
Main Methods:
- Density functional theory (DFT) calculations.
- Exploration of four crystal symmetries: P3[combining macron], C2/m, P3m1, and P3[combining macron]m1.
- Harmonic and anharmonic vibrational analyses.
- Comparison of calculated X-ray diffraction (XRD) patterns with experimental data.
Main Results:
- Calculated XRD patterns show good agreement with experimental results.
- Harmonic vibrational analysis indicates imaginary modes for most phases at 0 K.
- Anharmonic analysis reveals that only the C2/m phase is stable at room temperature.
- Other Mg(OH)2 phases become thermally competitive at elevated temperatures.
Conclusions:
- The C2/m phase of magnesium hydroxide is the most stable at room temperature.
- Anharmonic effects are crucial for understanding Mg(OH)2 stability.
- Temperature significantly influences the competitive stability of different Mg(OH)2 polymorphs.
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