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Phonon spectrum, thermal expansion and heat capacity of UO2 from first-principles

机译:第一性原理的UO2声子谱,热膨胀和热容

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摘要

We report first-principles calculations of the phonon dispersion spectrum, thermal expansion, and heat capacity of uranium dioxide. The so-called direct method, based on the quasiharmonic approximation, is used to calculate the phonon frequencies within a density functional framework for the electronic structure. The phonon dispersions calculated at the theoretical equilibrium volume agree well with experimental dispersions. The computed phonon density of states (DOSs) compare reasonably well with measured data, as do also the calculated frequencies of the Raman and infrared active modes including the LO/TO splitting. To study the pressure dependence of the phonon frequencies we calculate phonon dispersions for several lattice constants. Our computed phonon spectra demonstrate the opening of a gap between the optical and acoustic modes induced by pressure. Taking into account the phonon contribution to the total free energy of UO2 its thermal expansion coefficient and heat capacity have been computed from first-principles. Both quantities are in good agreement with available experimental data for temperatures up to about 500 K.
机译:我们报告声子弥散谱,热膨胀和二氧化铀的热容量的第一性原理计算。基于准谐波近似的所谓直接方法用于计算电子结构的密度函数框架内的声子频率。以理论平衡体积计算的声子色散与实验色散非常吻合。计算出的声子态密度(DOS)与测量数据相当吻合,拉曼和红外有源模式(包括LO / TO分裂)的计算频率也是如此。为了研究声子频率的压力依赖性,我们计算了几个晶格常数的声子色散。我们计算出的声子光谱证明了由压力引起的光学和声学模式之间的间隙的打开。考虑到声子对UO2的总自由能的贡献,已根据第一性原理计算了其热膨胀系数和热容量。两种量都与最高约500 K的温度的可用实验数据高度吻合。

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