Despite the growing interest in apatites, available experimental studies on their properties are limited in scope. Researchers, therefore, are increasingly resorting to predictions using the density functional theory (DFT). However, large deviations can be seen between DFT based estimates and experimental results, presumably due to approximations made in DFT models. We undertake a comprehensive benchmarking exercise involving sixteen exchange-correlation (XC) functionals (including dispersion corrections), five pseudopotentials (PPs), and two basis sets to unravel their best combination for studying apatites. The comparison involves lattice parameters, elastic constants, bulk modulus, and band gap of three specific apatites -- hydroxyapatite, fluorapatite and chlorapatite. We show, quite reassuringly, a weak sensitivity of the properties to the choice of PP and the basis. The XC approximation and/or the inclusion of the dispersion corrections has significant influence on the accuracy of predicted properties. The underlying reasons behind different XC functionals providing different properties are identified. Our recommendation is to use dispersion corrections in XC functionals for studying apatites but with some caution. Overall, the optB86b-vdW functional provides the best accuracy when compared to the available experimental results.

中文翻译：

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对 DFT 近似值进行基准测试，用于研究磷灰石


尽管人们对 apatites 的兴趣日益浓厚，但关于其特性的现有实验研究范围有限。因此，研究人员越来越多地求助于使用密度泛函理论 （DFT） 进行预测。然而，在基于 DFT 的估计值和实验结果之间可以看到很大的偏差，这可能是由于 DFT 模型中的近似值。我们进行了一项全面的基准测试，涉及 16 个交换相关 （XC） 泛函（包括色散校正）、5 个赝势 （PP） 和 2 个基集，以揭示它们用于研究 apatites 的最佳组合。比较涉及三种特定磷灰石（羟基磷灰石、氟磷灰石和氯磷灰石）的晶格参数、弹性常数、体积模量和带隙。我们非常令人欣慰地表明，特性对 PP 的选择和基础的敏感性较弱。XC 近似和/或包含色散校正对预测属性的准确性有重大影响。确定了不同 XC 功能提供不同特性背后的根本原因。我们建议在 XC 泛函中使用色散校正来研究磷灰石，但要谨慎。总体而言，与可用的实验结果相比，optB86b-vdW 函数提供了最佳的准确性。