Spin crossover materials are bi-stable systems with potential applications as molecular scale electronic switches, actuators, thermometers, barometers, and displays. However, calculating the enthalpy difference, ΔH, between the high spin and low spin states has been plagued with difficulties. For example, many common density functional theory (DFT) methods fail to even predict the correct sign of ΔH, which determines the low temperature state. Here, we study a collection of Fe(II) and Fe(III) materials, where ΔH has been measured, which has previously been used to benchmark density functionals. The best performing hybrid functional, TPSSh, achieves a mean absolute error compared to experiment of 11 kJ mol⁻¹ for this set of materials. However, hybrid functionals scale badly in the solid state; therefore, local functionals are preferable for studying crystalline materials, where the most interesting spin crossover phenomena occur. We show that both the Liechtenstein and Dudarev DFT+U methods are a little more accurate than TPSSh. The Dudarev method yields a mean absolute error of 8 kJ mol⁻¹ for U_eff = 1.6 eV. However, the mean absolute error for both TPSSh and DFT+U is dominated by a single material, for which the two theoretical methods predict similar enthalpy differences—if this is excluded from the set, then DFT+U achieves chemical accuracy. Thus, DFT+U is an attractive option for calculating the properties of spin crossover crystals, as its accuracy is comparable to that of meta-hybrid functionals, but at a much lower computational cost.

中文翻译：

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DFT + U中自旋交越晶体的快速，准确的焓差。

自旋交叉材料是双稳态系统，具有潜在的应用前景，如分子规模的电子开关，执行器，温度计，气压计和显示器。然而，计算高自旋状态和低自旋状态之间的焓差ΔH一直很困难。例如，许多常见的密度泛函理论（DFT）方法甚至都无法预测确定低温状态的ΔH的正确符号。在这里，我们研究了一组Fe（II）和Fe（III）材料，其中已测量了ΔH，该材料以前已用于基准密度函数。与11 kJ mol ^-1的实验相比，性能最佳的混合功能TPSSh可实现平均绝对误差对于这套材料。但是，混合功能在固态时会严重缩放。因此，对于研究最有趣的自旋交叉现象的晶体材料而言，局部功能是更可取的。我们显示，列支敦士登和杜达列夫DFT + U方法都比TPSSh准确一些。对于U _eff，Dudarev方法产生的平均绝对误差为8 kJ mol ^-1= 1.6 eV。然而，TPSSh和DFT + U的平均绝对误差均由一种材料决定，这两种理论方法均预测出相似的焓差-如果将其排除在外，则DFT + U可获得化学精度。因此，DFT + U是计算自旋交叉晶体特性的一种有吸引力的选择，因为它的精度可与亚杂化功能相媲美，但计算成本却低得多。