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Anharmonicity and Phase Diagram of Magnesium Oxide in the Megabar Regime

Journal Article · · Physical Review Letters
 [1];  [2]
  1. Univ. of California, Berkeley, CA (United States); École Normale Supérieure de Lyon (France); CEA DAM-DIF, Arpajon (France); The Regents of the University of California; University of California, San Diego
  2. Univ. of California, Berkeley, CA (United States)
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With density functional molecular dynamics simulations, we computed the phase diagram of MgO from 50 to 2000 GPa up to 20000 K. Via thermodynamic integration (TDI), we derive the Gibbs free energies of the B1, B2, and liquid phases and determine their phase boundaries. With TDI and a pseudo-quasi-harmonic approach, we show that anharmonic effects are important and stabilize the B1 phase in particular. As a result, the B1-B2 transition boundary in the pressure-temperature plane exhibits a steep slope. We predict the B1-B2-liquid triple point to occur at approximately T= 10000 K and P = 370 GPa, which is higher in pressure than was inferred with quasi-harmonic methods alone. We predict the principal shock Hugoniot curve to enter the B2 phase stability domain but only over a very small range of parameters. Here, this may render it difficult to observe this phase with shock experiments because of kinetic effects.
Research Organization:
Univ. of California, San Diego, La Jolla, CA (United States)
Sponsoring Organization:
USDOE National Nuclear Security Administration (NNSA); National Science Foundation
Grant/Contract Number:
NA0003842; SC0016248
OSTI ID:
1784846
Journal Information:
Physical Review Letters, Journal Name: Physical Review Letters Journal Issue: 17 Vol. 125; ISSN 0031-9007
Publisher:
American Physical Society (APS)Copyright Statement
Country of Publication:
United States
Language:
English

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Related Subjects

3-dimensional systems
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
Ab initio calculations
Anharmonic lattice dynamics
Crystalline systems
Density functional theory
Entropy
First-principles calculations
Lattice dynamics
Liquid-solid phase transition
Liquids
Molecular dynamics
Phase diagrams
Phase transitions
Single crystal materials
Solid-solid transformations