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arXiv 0903.4926cond-mat.mtrl-scicond-mat.soft
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加压下甲烷的理论研究

Theoretical investigation of methane under pressure

Leonardo Spanu, Davide Donadio, Detlef Hohl, Giulia Galli

备注：
to appear on Journ. Chem. Phys
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摘要：

我们提出了计算机模拟的液相和固相的冷凝甲烷在压力低于25 GPa，150和300 K之间，没有明显的分子解离发生。我们使用分子动力学（MD）和metadaptics技术，和经验的潜力，在刚性分子近似，其有效性证实了后验进行从头算MD模拟选定的压力和温度条件。我们的结果与现有的测量结果是令人满意的协议。结果表明，在10 GPa和150 K时，fcc晶体转变为hcp结构，每晶胞4个分子（B相），在20 GPa以上，B相转变为单斜相。固/固相变的结果是一致的拉曼研究，但在我们的计算中估计的相边界是在更高的压力比那些从光谱数据推断。

英文摘要：

We present computer simulations of liquid and solid phases of condensed methane at pressures below 25 GPa, between 150 and 300 K, where no appreciable molecular dissociation occurs. We used molecular dynamics (MD) and metadynamics techniques, and empirical potentials in the rigid molecule approximation, whose validity was confirmed a posteriori by carrying out it ab initio MD simulations for selected pressure and temperature conditions. Our results for the melting line are in satisfactory agreement with existing measurements. We find that the fcc crystal transforms into a hcp structure with 4 molecules per unit cell (B phase) at about 10 GPa and 150 K, and that the B phase transforms into a monoclinic high pressure phase above 20 GPa. Our results for solid/solid phase transitions are consistent with those of Raman studies but the phase boundaries estimated in our calculations are at higher pressure than those inferred from spectroscopic data.

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