Theoretical and computational study on molecular hydrodynamics through molecular dynamics

Abstract

Hydrodynamic and thermodynamic properties of simple fluids have been theoretically and numerically studied through molecular dynamics simulations. We constructed the vector field representing the flow pattern around a tagged particle from not only equilibrium but also nonequilibrium molecular dynamics simulations. This vector field was decomposed into the sum of a longitudinal, and a transverse vector field with the help of the Helmholtz decomposition. We were able to assess quantitatively the applicability and limitations of the hydrodynamics descriptions based on the linearized Navier-Stokes theory. We formulated the density fluctuation equation using the memory function approach. The space-dependent diffusion coefficient of a tagged particle was investigated via memory function approach and made an analogy with the fluctuating hydrodynamics theory. A numerical method which generate a colored Gaussian noise was developed, and compared with the fluctuating forces obtained from MD simulations. We have examined the error of various method when calculating the memory kernel using data containing noise. We derive an analytical expression of the second virial coefficient of d-dimensional hard sphere fluids confined to slit pores. We present an analytical form of thermodynamic functions such as entropy and pressure tensor as a function of the size of the slit pore. Molecular dynamics simulations are performed, and the results are compared with analytically obtained equations of state. We investigate the energetics involved in the tension and compression twinning deformation processes in magnesium via first-principles studies. Through identification of structural changes associated with each deformation process, we study the energetics of each deformation process and the local instability in the twin boundary region. We extend our study to examine the effects of Y and Li as alloying elements on each twinning deformation process. Our calculations predict that the addition of Y causes a weakening of the resistivity to twinning deformation