Bafile Ubaldo, Guarini Eleonora, Sampoli Marco, Barocchi Fabrizio
Consiglio Nazionale delle Ricerche, Istituto dei Sistemi Complessi, via Madonna del Piano 10, I-50019 Sesto Fiorentino, Italy.
Phys Rev E Stat Nonlin Soft Matter Phys. 2009 Oct;80(4 Pt 1):040201. doi: 10.1103/PhysRevE.80.040201. Epub 2009 Oct 12.
Molecular-dynamics calculations of the translational dynamic structure factor in liquid CO2 and CD4 are analyzed by means of the generalized Langevin equation for the intermediate scattering function in the second-order memory function approximation. We give a rigorous general relation among the decay times of the memory and the lifetimes of the modes of the density-density correlation function. The comparison of the various characteristic times among them and with the collision time, carried out as a function of the wave vector, reveals strong relationships between the memory relaxation and the density-density correlation modes, some of which have purely "collisional" and other "collective" character. We show that essential information about the life time of structural properties in a molecular liquid at nanometer dimensions can be obtained if the time behavior of the correlation function is considered in addition to that of the memory function.
利用二阶记忆函数近似下中间散射函数的广义朗之万方程，分析了液态CO₂和CD₄中平移动态结构因子的分子动力学计算。我们给出了记忆衰减时间与密度-密度关联函数模式寿命之间严格的一般关系。作为波矢的函数，对它们之间以及与碰撞时间的各种特征时间进行比较，揭示了记忆弛豫与密度-密度关联模式之间的强关系，其中一些具有纯粹的“碰撞”特征，另一些具有“集体”特征。我们表明，如果除了记忆函数的时间行为外，还考虑关联函数的时间行为，就可以获得关于纳米尺寸分子液体中结构性质寿命的基本信息。
