Department of Physics, Kyushu University, Fukuoka 819-0395, Japan.
J Chem Phys. 2018 May 21;148(19):194702. doi: 10.1063/1.5022319.
In the calculations of tetragonal BaTiO, some exchange-correlation (XC) energy functionals such as local density approximation (LDA) have shown good agreement with experiments at room temperature (RT), e.g., spontaneous polarization ( ), and superiority compared with other XC functionals. This is due to the error compensation of the RT effect and, hence, will be ineffective in the heavily strained case such as domain boundaries. Here, ferroelectrics under large strain at RT are approximated as those at 0 K because the strain effect surpasses the RT effects. To find effective XC energy functionals for strained BaTiO, we propose a new comparison, i.e., a criterion. This criterion is the properties at 0 K given by the Ginzburg-Landau (GL) theory because GL theory is a thermodynamic description of experiments working under the same symmetry-constraints as calculations. With this criterion, we examine LDA, generalized gradient approximations (GGA), meta-GGA, meta-GGA + local correlation potential (), and hybrid functionals, which reveals the high accuracy of some XC functionals superior to XC functionals that have been regarded as accurate. This result is examined directly by the calculations of homogenously strained tetragonal BaTiO, confirming the validity of the new criterion. In addition, the data points of theoretical vs. certain crystallographic parameters calculated with different XC functionals are found to lie on a single curve, despite their wide variations. Regarding these theoretical data points as corresponding to the experimental results, analytical expressions of the local using crystallographic parameters are uncovered. These expressions show the primary origin of BaTiO ferroelectricity as oxygen displacements. Elastic compliance and electrostrictive coefficients are estimated. For the comparison of strained results, we show that the effective critical temperature under strain <-0.01 is >1000 K from an approximate method combining results with GL theory. In addition, in a definite manner, the present results show much more enhanced ferroelectricity at large strain than the previous reports.
在四方 BaTiO 的计算中，一些交换关联（XC）泛函，如局域密度近似（LDA），在室温（RT）下与实验表现出良好的一致性，例如自发极化（），并且优于其他 XC 泛函。这是由于 RT 效应的误差补偿，因此在像畴壁这样的强应变情况下将无效。在这里，RT 下的大应变铁电体被近似为 0 K 下的铁电体，因为应变效应超过了 RT 效应。为了找到适用于应变 BaTiO 的有效 XC 泛函，我们提出了一种新的比较，即一个准则。这个准则是由 Ginzburg-Landau（GL）理论给出的 0 K 时的性质，因为 GL 理论是在与 XC 计算相同的对称约束下进行的实验的热力学描述。使用这个准则，我们检验了 LDA、广义梯度近似（GGA）、meta-GGA、meta-GGA+局部相关势（）和混合泛函，发现一些 XC 泛函的精度非常高，优于被认为准确的 XC 泛函。通过对均匀应变四方 BaTiO 的计算直接检验了这一结果，证实了新准则的有效性。此外，发现不同 XC 泛函计算得到的理论值与某些晶体学参数之间的数据点落在一条单独的曲线上，尽管它们的变化范围很广。将这些理论数据点视为对应于实验结果，揭示了使用晶体学参数的局部值的解析表达式。这些表达式表明 BaTiO 铁电性的主要起源是氧位移。弹性柔顺性系数和电致伸缩系数也被估计出来。对于应变结果的比较，我们展示了一种结合 GL 理论和的近似方法，在应变<-0.01 下有效临界温度是>1000 K。此外，以确定的方式，本结果显示在大应变下的铁电性比以前的报告有了更大的增强。
