Ab initio lattice dynamics and thermal expansion of Cu 2 O
Ab initio lattice dynamics and thermal expansion of Cu 2 O
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DOI：
10.1103/physrevb.80.134304
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发表时间：
2009-10
影响因子：
3.7
通讯作者：
K. Bohnen;R. Heid;L. Pintschovius;Aloysius Soon;C. Stampfl
中科院分区：
文献类型：
--
作者：
K. Bohnen;R. Heid;L. Pintschovius;Aloysius Soon;C. Stampfl
用从头算密度泛函微扰理论研究了Cu2O的晶格动力学。与较老的中子散射结果的差异引发了我们自己的中子散射调查，这证实了理论预测。在精确描述声子色散的基础上，计算了自由能的振动部分作为晶格常数和温度的函数。热膨胀实验结果与实验结果吻合较好。对于T300K，观察到负的热膨胀，而在更高的温度下，获得了正常的热膨胀。NTE的产生是由于能量为20 meV的声子模的反常行为，该声子模对模式和波矢高度敏感。我们的计算还表明，基于精确声子色散的自由能与基于广泛使用的爱因斯坦模型描述的自由能相差超过20%，这清楚地表明了适当的声子色散处理对于获得可靠的热力学数据的重要性。
Using ab initio density-functional perturbation theory the lattice dynamics of Cu2O has been extensively studied. Discrepancies with older neutron-scattering results triggered a neutron-scattering investigation of our own which confirmed the theoretical prediction. Based on the accurate description of the phonon dispersion the vibrational part of the free energy was calculated as a function of lattice constant and temperature. The thermal expansion could be obtained in good agreement with experiments. For T300 K negative thermal expansion NTE was observed while for higher temperatures normal thermal expansion was obtained. The origin of the NTE is due to anomalous behavior of phonon modes with energies 20 meV which is highly mode and wave-vector sensitive. Our calculations also showed that free energies based on the exact phonon dispersion and those based on an Einstein-model description widely used differed by more than 20%, which clearly indicates the importance of proper phonon-dispersion treatment for obtaining reliable thermodynamic data.