We use extensive first-principles quantum mechanical calculations to show that, although the static lattice and harmonic vibrational energies are almost identical, the anharmonic vibrational energy of hexagonal ice is significantly lower than that of cubic ice. This difference in anharmonicity is crucial, stabilizing hexagonal ice compared with cubic ice by at least 1.4 meV / H 2 O , in agreement with experimental estimates. The difference in anharmonicity arises predominantly from molecular O-H bond-stretching vibrational modes and is related to the different stacking of atomic layers.
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机译：我们使用大量的第一性原理量子力学计算表明，尽管静态晶格和谐波振动能几乎相同，但六角形冰的非谐振动能明显低于立方冰。非谐性上的这种差异至关重要，与实验估计值相比，与立方冰相比，六角形冰至少稳定了1.4 meV / H 2O。非谐性的差异主要是由分子的O-H键拉伸振动模式引起的，并且与原子层的不同堆积有关。
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