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. This may render it difficult to observe this phase with shock experiments because of kinetic effects.

中文翻译：

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氧化镁在兆巴态下的非调和相图

通过密度泛函分子动力学模拟，我们计算了MgO从50到2000 GPa至20000 K的相图。通过热力学积分（TDI），我们得出B1，B2和液相的吉布斯自由能，并确定它们的相边界。使用TDI和拟准谐波方法，我们表明非谐波效应非常重要，尤其可以稳定B1相。结果，压力-温度平面中的B1-B2过渡边界表现出陡峭的斜率。我们预测B1-B2-液体三相点将在大约T = 10000 K和P = 370 GPa处发生，这比单独使用准谐波方法推断的压力要高。我们预测主冲击休格尼奥特曲线进入B2相稳定域，但仅在很小的参数范围内。