熔融氯化钠晶体介电常数的模拟计算方法

A simulation method for calculating the dielectric constant of molten sodium chloride crystals

由于分子模拟过程中存在周期性边界的影响,离子偶极矩定义模糊,导致传统的偶极矩涨落方法在计算熔融盐晶体或含有自由电荷体系的介电常数时存在一定阻碍。根据经典介电理论,通过电流关联函数计算熔融氯化钠(NaCl)晶体体系的介电常数,研究了不同温度下氯化钠的频率相关介电谱,并分析了晶体相变对介电特性的影响。结果表明:当NaCl为晶体状态时,介电谱显示出明显的共振吸收峰;在NaCl熔化以后,介电谱的共振吸收峰的带宽变宽,波形发生了明显变化。分别利用电流法和外加电场法计算了不同温度下NaCl的静态介电常数,结果显示:两种方法的计算结果的一致性良好,从而验证了本文方法的准确性;NaCl晶体在发生固液相变时,静态介电常数会在相变点发生跳变。

Due to the influence of periodic boundaries in the molecular simulation process,the definition of the dipole moment of ions is fuzzy,which leads to some obstacles in calculating the dielectric constant of molten salt crystals or the free charge system in solution using the traditional dipole moment fluctuation method.According to classical dielectric theory,the dielectric constant of the molten sodium chloride(NaCl)crystal system was calculated using the current correlation function.The frequency-dependent dielectric spectra of NaCl at different temperatures were studied,and the influence of the crystal phase transition on the dielectric properties was analyzed.When NaCl is in the crystal state,the dielectric spectra show an obvious resonance absorption peak.After melting,the bandwidth of the resonance absorption peak of the dielectric spectrum of NaCl becomes broader,and the waveform changes significantly.The static dielectric constants of NaCl at different temperatures were calculated using the current correlation method and the external applied electric field method.The calculated results of the two methods are in good agreement,which verifies the accuracy of our method.When the NaCl crystal undergoes a solid-liquid phase transition,the static dielectric constant shows a sudden jump at the phase transition point.