Brandt Erik G, Edholm Olle
Theoretical Biological Physics, Department of Theoretical Physics, Royal Institute of Technology (KTH), AlbaNova University Center, Stockholm, Sweden.
Biophys J. 2009 Mar 4;96(5):1828-38. doi: 10.1016/j.bpj.2008.11.044.
Dynamic structure factors for a lipid bilayer have been calculated from molecular dynamics simulations. From trajectories of a system containing 1024 lipids we obtain wave vectors down to 0.34 nm(-1), which enables us to directly resolve the Rayleigh and Brillouin lines of the spectrum. The results confirm the validity of a model based on generalized hydrodynamics, but also improves the line widths and the position of the Brillouin lines. The improved resolution shows that the Rayleigh line is narrower than in earlier studies, which corresponds to a smaller thermal diffusivity. From a detailed analysis of the power spectrum, we can, in fact, distinguish two dispersive contributions to the elastic scattering. These translate to two exponential relaxation processes in separate time domains. Further, by including a first correction to the wave-vector-dependent position of the Brillouin lines, the results agree favorably to generalized hydrodynamics even up to intermediate wave vectors, and also yields a 20% higher adiabatic sound velocity. The width of the Brillouin lines shows a linear, not quadratic, dependence to low wave vectors.
已通过分子动力学模拟计算出脂质双层的动态结构因子。从包含1024个脂质的系统轨迹中，我们获得了低至0.34 nm⁻¹ 的波矢，这使我们能够直接分辨光谱的瑞利线和布里渊线。结果证实了基于广义流体动力学的模型的有效性，但同时也改善了线宽和布里渊线的位置。更高的分辨率表明，瑞利线比早期研究中的更窄，这对应于更小的热扩散率。通过对功率谱的详细分析，实际上我们可以区分弹性散射的两种色散贡献。这转化为在不同时域中的两个指数弛豫过程。此外，通过对布里渊线的波矢相关位置进行首次校正，即使在中等波矢下，结果也与广义流体动力学非常吻合，并且绝热声速提高了20%。布里渊线的宽度对低波矢呈线性而非二次依赖性。
