Theiss Research, P. O. Box 127, La Jolla, California 92038, USA.
Material Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Dr., Gaithersburg, Maryland 20899, USA.
J Chem Phys. 2023 Mar 28;158(12):124122. doi: 10.1063/5.0143425.
We demonstrate a method to compute the dielectric spectra of fluids in molecular dynamics (MD) by directly applying electric fields to the simulation. We obtain spectra from MD simulations with low magnitude electric fields (≈0.01 V/Å) in agreement with spectra from the fluctuation-dissipation method for water and acetonitrile. We examine this method's trade-off between noise at low field magnitudes and the nonlinearity of the response at higher field magnitudes. We then apply the Booth equation to describe the nonlinear response of both fluids at low frequency (0.1 GHz) and high field magnitude (up to 0.5 V/Å). We develop a model of the frequency-dependent nonlinear response by combining the Booth description of the static nonlinear dielectric response of fluids with the frequency-dependent linear dielectric response of the Debye model. We find good agreement between our model and the MD simulations of the nonlinear dielectric response for both acetonitrile and water.
我们展示了一种通过直接向模拟施加电场来计算分子动力学 (MD) 中流体介电谱的方法。我们通过在 MD 模拟中施加低幅度电场 (≈0.01 V/Å) 获得了与水和乙腈的涨落耗散方法得出的光谱一致的光谱。我们研究了这种方法在低场幅度下的噪声与在更高场幅度下的响应非线性之间的权衡。然后，我们应用 Booth 方程来描述这两种流体在低频 (0.1 GHz) 和高场幅度 (高达 0.5 V/Å) 下的非线性响应。我们通过将 Booth 对流体静态非线性介电响应的描述与 Debye 模型的频率相关线性介电响应相结合，开发了一种频率相关非线性响应模型。我们发现，我们的模型与乙腈和水的非线性介电响应的 MD 模拟之间有很好的一致性。
