Instituto de Física, Universidade Federal do Rio Grande do Sul, Caixa Postal 15051, CEP 91501-970, Porto Alegre, RS, Brazil and Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany.
J Chem Phys. 2018 May 21;148(19):193829. doi: 10.1063/1.5013337.
We study, using Monte Carlo simulations, the density profiles and differential capacitance of ionic liquids confined by metal electrodes. To compute the electrostatic energy, we use the recently developed approach based on periodic Green's functions. The method also allows us to easily calculate the induced charge on the electrodes permitting an efficient implementation of simulations in a constant electrostatic potential ensemble. To speed up the simulations further, we model the ionic liquid as a lattice Coulomb gas and precalculate the interaction potential between the ions. We show that the lattice model captures the transition between camel-shaped and bell-shaped capacitance curves-the latter characteristic of ionic liquids (strong coupling limit) and the former of electrolytes (weak coupling). We observe the appearance of a second peak in the differential capacitance at ≈0.5 V for 2:1 ionic liquids, as the packing fraction is increased. Finally, we show that ionic size asymmetry decreases substantially the capacitance maximum, when all other parameters are kept fixed.
我们使用蒙特卡罗模拟研究了金属电极限制的离子液体的密度分布和微分电容。为了计算静电能，我们使用了最近基于周期性格林函数开发的方法。该方法还允许我们轻松计算电极上的感应电荷，从而可以在恒定静电势系综中有效地实现模拟。为了进一步加快模拟速度，我们将离子液体建模为晶格库仑气体，并预先计算离子之间的相互作用势。我们表明，晶格模型捕捉到了电容曲线从骆驼形到钟形的转变——后者是离子液体的特征（强耦合极限），而前者是电解质的特征（弱耦合）。我们观察到，当增加 2:1 离子液体的堆积分数时，在 ≈0.5 V 处微分电容出现第二个峰值。最后，我们表明，当所有其他参数保持不变时，离子大小不对称性大大降低了电容最大值。
