Identifying systematic errors in a power spectral analysis of simulated lipid membranes
Identifying systematic errors in a power spectral analysis of simulated lipid membranes
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DOI：
10.1063/5.0049448
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发表时间：
2021-06-07
影响因子：
4.4
通讯作者：
Deserno, Markus
中科院分区：
文献类型：
--
作者：
Erguder, Muhammed F.;Deserno, Markus
脂质膜的弹性特性可以通过监测其热波动来测量。例如，将膜形状或脂质导向器波动的功率谱与基于合适的连续介质理论的预测进行比较，可以获得弯曲模量、倾斜模量和扭曲模量。然而，要在计算机模拟中做到这一点，我们必须首先从一个通常相当小的盒子中的脂质分子的离散配置定义连续表面形状和脂质导向场。在这里，我们表明所需的映射选择以及后续数据分析的细节可以使这些模量的测量值的变化远远超过其统计不确定性。我们根据 13 种不同脂质的原子模拟轨迹研究了由此产生的系统误差，该轨迹由 Venable 等人先前发表。 [化学。物理。脂质 192, 60-74 (2015)]。具体来说，我们检查表面场和倾斜场定义的映射选择，标准化和平均脂质导向器，考虑波矢量相关的时间自相关，误差传播，并找到正确的拟合范围。我们提出了一组标准，可以帮助决定波动分析背后的特定选择组合，并根据这些标准提出一些建议。虽然原则上，对于足够大的系统尺寸，从大波长限制中提取的可观测量的系统偏移会消失，但对于本质局部参数（例如扭转模量或张开倾斜耦合）而言，不存在这种精确的限制，因此并非所有潜在的选择都可以简单地验证。
The elastic properties of lipid membranes can be measured by monitoring their thermal fluctuations. For instance, comparing the power spectra of membrane shape or lipid director fluctuations with predictions based on suitable continuum theories gives access to bending-, tilt-, and twist-moduli. However, to do so in a computer simulation, we must first define a continuum surface shape and lipid director field from the discrete configurations of lipid molecules in a typically fairly small box. Here, we show that the required mapping choices, as well as the details of the subsequent data analysis, can shift the measured values of these moduli by far more than their statistical uncertainties. We investigate the resulting systematic errors on the basis of atomistic simulation trajectories for 13 different lipids, previously published by Venable et al. [Chem. Phys. Lipids 192, 60-74 (2015)]. Specifically, we examine mapping choices for surface- and tilt-field definitions, normalizing and averaging lipid directors, accounting for wave vector dependent time autocorrelations, error propagation, and finding the right fitting range. We propose a set of criteria that may help to decide upon a particular combination of choices underlying the fluctuation analysis, and we make several recommendations based on these. While systematic shifts in observables that are extracted from large-wavelength limits vanish, in principle, for sufficiently large system size, no such exact limit exists for intrinsically local parameters, such as the twist modulus or the splay-tilt coupling, and so not all potential choices can be trivially verified.