| There are different computational techniques that are designed to fit particular applications. One of them is molecular dynamics (MD) simulation. We use MD to study a system of particles polydisperse in both size and mass and test for and quantify systematic changes in dynamical properties that result from polydispersity. Our results elucidate the interpretation of experimental studies of collective particle motion in colloids, and we discuss the implications of polydispersity for observations of dynamical heterogeneity, in both simulations of simple liquids and colloid experiments. To isolate the effect of mass alone, we studied isotope mixtures. The velocity autocorrelation function changes greatly when the mass difference of two species increases.;The "long-time tails", the nonexponential decay of a velocity autocorrelation function, gave rise to many questions. One of them is the correctness of the explanation of the real motion of molecules in fluid by introducing hydrodynamic models. We found that the hydrodynamic interpretation has limitations in describing the motion of particles of molecular size.;It is suggested that a band-gap engineered to the shape of a Sech-squared potential can help to accurately determine band offsets in semiconductor heterojunctions, in separating conduction band carriers from valence band carriers, and is also useful in reducing noise in resonance tunneling and other devices.;The specific features of scattering of a Gaussian wave packet by the simplest of all reflectionless potentials, the Sech-squared well, are considered. The results of numerical computation show that a wave packet that has passed through this potential overtakes a free wave packet and is both higher and narrower than a free wave packet; in other words, the scattered wave packet accelerates inside the well and preserves its shape better. Comparisons with scattering by the square well and by a series of reflectionless potentials are also presented.;Molecular-beam epitaxy makes it possible to grow heterostructures of different semiconductor materials with controlled concentration of one component in order to tailor different potential profiles. We propose a device simulation using the inverse scattering method. It gives the well-defined procedure on how to recover a potential and wave functions from bound states at arbitrarily adjustable energies. It is possible, using the computer simulations, to find in advance which kind of a potential profile has to be grown so that this heterojunction device will be constructed to have desired properties. |
