We apply van der Waals density-functional theory (vdW-DFT) calculations to predict crystal structure parameters and spontaneous polarization values for seven hydrogen-bonded single-component organic ferroelectrics. The results show good agreement with experimental results, implying that an important step for the computational materials design of organic ferroelectrics has been achieved. This approach also enables the simulation of electromechanical responses. Calculations using the vdW-DFT method are performed for croconic acid (CRCA), 2-phenylmalondialdehyde (PhMDA), and 5,6-dichloro-2-methylbenzimidazole (DC-MBI) under uniaxial stresses or electric fields. Direct piezoelectric $d_{33}$ constants are evaluated from the polarization change as a function of stress, whereas converse piezoelectric $d_{33}$ constants are evaluated from the change in lattice parameter as a function of electric field. The obtained values show acceptable agreement with the experimental values if possible objective factors are considered. The stress-induced or electric-field-induced variation of polarization is analyzed considering two types of contributions. One is from proton transfer as a classical point charge motion and the other residual part corresponds to the redistribution of $\pi$ electrons.

中文翻译：

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范德华密度泛函理论计算重新审视氢键单组分有机铁电体

我们应用范德华密度泛函理论 (vdW-DFT) 计算来预测七个氢键单组分有机铁电体的晶体结构参数和自发极化值。结果与实验结果吻合良好，表明有机铁电体的计算材料设计迈出了重要的一步。这种方法还可以模拟机电响应。在单轴应力或电场下，使用 vdW-DFT 方法对克罗康酸 (CRCA)、2-苯基丙二醛 (PhMDA) 和 5,6-二氯-2-甲基苯并咪唑 (DC-MBI) 进行计算。直接压电$d_{33}$ 常数是根据作为应力函数的极化变化来评估的，而逆压电 $d_{33}$根据作为电场函数的晶格参数变化来评估常数。如果考虑可能的客观因素，获得的值与实验值显示可接受的一致性。考虑两种类型的贡献来分析应力引起的或电场引起的极化变化。一个来自质子转移作为经典的点电荷运动，另一个剩余部分对应于$\pi$ 电子。