Density functional calculations of the formation and migration enthalpies of monovacancies in Ni: Comparison of local and nonlocal approaches
Density functional calculations of the formation and migration enthalpies of monovacancies in Ni: Comparison of local and nonlocal approaches
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DOI：
10.1103/physrevb.74.064111
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发表时间：
2006-08
影响因子：
3.7
通讯作者：
E. H. Megchiche;S. Pérusin;J. Barthelat;C. Mijoule
中科院分区：
文献类型：
--
作者：
E. H. Megchiche;S. Pérusin;J. Barthelat;C. Mijoule
在这项工作中，我们考察了用于密度泛函理论方法的势和泛函，以便正确地描述镍中单空位的形成和迁移能。由于在实验上不能很好地知道在$0\Pantom{{0.3em}{0ex}}\mathm{K}中的形成热，我们在第一步中选择确定块体的一些结构、磁性和弹性性质，这些性质已经在实验上得到了很好的证实。对局域自旋密度近似(LSDA)和广义梯度近似(GGA)交换关联泛函两种方法进行了比较。我们的结论是，为了正确地描述电子密度，非定域GGA项的贡献对于确定单空位的形成和迁移热和活化能是必要的。两种方法计算的构型和迁移量都有很大的差异。与GGA近似相比，LSDA近似的高估为：${H}_{v}^{f}$的$0.25\phantom{\Rule{0.3em}{0ex}}\mathrm{ev}$和${h}_{v}^{m}$的$0.23\phantom{\Rule{0.3em}{0ex}}\mathm{ev}$，导致激活能${q}_{1}$的两种方法之间存在$0.48\phantom{\Rule{0.3em}{0ex}}\mathm{ev}$的差距。结果表明，如果通过晶格参数的变化来考虑热膨胀的贡献，GGA的结果与实验数据具有可比性。结果表明，活化能几乎不受热膨胀效应的影响，因此可以预期，扩散因子在熔点附近的Arrhenius曲线曲率本质上是双空位贡献的结果。
We examine in this work the potential and the functional to be used in a density functional theory approach in order to describe correctly the formation and migration energies of monovacancies in nickel. As the formation enthalpy is not well-known experimentally at $0\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, we choose in a first step to determine some structural, magnetic, and elastic properties of the bulk, which are well-established experimentally. The comparison between both approaches, i.e., the local spin density approximation (LSDA) and the generalized gradient approximation (GGA) exchange-correlation functionals is analyzed. We conclude that the contribution of nonlocal GGA terms in order to describe correctly the electronic density is necessary to determine the formation and migration enthalpies and activation energy of monovacancy. The calculated formation ${H}_{v}^{f}$ and migration ${H}_{v}^{m}$ enthalpies differ significantly between both approaches. The overestimation of the LSDA approximation is of $0.25\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ for ${H}_{v}^{f}$ and of $0.23\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ for ${H}_{v}^{m}$ with respect to the GGA one, leading to a gap of $0.48\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ between both methods for the activation energy ${Q}_{1}$. We show that the GGA results are comparable with experimental data if the thermal expansion contribution is taken into account through the lattice parameter variation. Finally, it is shown that the activation energy is nearly independent of the thermal expansion effects; thus we can expect that the curvature of the Arrhenius plot of the diffusion factor near the melting point is essentially due to the contribution of divacancies.