Realistic Implementation of the Particle Model for the Visualization of Nanoparticle Precipitation and Growth

Abstract

An application for visualizing the aggregation of structureless atoms is presented. The application allows us to demonstrate on a qualitative basis, as well as by quantitatively monitoring the aggregate surface/volume ratio, that the enhanced reactivity of nanoparticles can be connected with their large specific surface. It is suggested that, along with the use of geometric analogies, this bottom-up approach can be effective in discussing the enhanced reactivity proprieties of nanoparticles. The application is based on a two-dimensional realistic dynamic model where atoms move because of their thermal and interaction potential energies, and the trajectories are determined by solving numerically Newton’s laws according to a Molecular Dynamics (MD) scheme. For this purpose, a web-based MD engine was adapted as needed. It is suggested that, when possible, using a realistic simulation rather than simple animations offers several advantages in the visualization of processes of interest in chemistry education. First, in a simulation the outcome of the process under study is not set a priori but it is the result of the dynamic evolution of the system; furthermore, specific parameters can be systematically varied, and the effects of these changes can be investigated. The application can be used at different levels of detail and in different instruction levels. Qualitative visual observations of the growing aggregates and of the progressive decrease of the reactive surface are suitable at all levels of instruction. Systematic investigations on the effect of changes of the atomic and aggregate sizes and temperature, suitable for senior high school and college courses, are also reported.

Elucidating the Influence of the Activation Energy on Reaction Rates by Simulations Based on a Simple Particle Model

“…For the reasons discussed in previous work, , in order to describe and visualize the dynamical behavior of the particle model of matter, rather than use arbitrary animations, in this work a realistic model based on the Molecular Dynamics (MD) method has been adopted. In this way, in addition to the didactical advantage of demonstrating how a theoretical model can provide quantitative tools by the use of explicit physical laws, control parameters can be changed systematically in order to investigate the effects on the results.…”

“…In an MD simulation, the position and velocity of each atom can be calculated, for a given time step d t = 1 fs, by solving numerically Newton’s equations of motion. Full details about the MD procedure can be found in previous work , and in the specialized literature. , In this work, a web-based MD engine was used.…”

“…In principle, an MD simulation can be performed in two or three dimensions, with the latter being more realistic but computationally substantially more demanding. 18 In this work, in order to minimize the computing time and, thus, run the application interactively, a 2D environment was adopted.…”

“…The application can be used to elucidate the energetics involved in chemical kinetics. As we have already pointed out, , previous studies have used simplified animations where the dynamics were chosen arbitrarily. Here, we expand upon this by introducing a Molecular Dynamics (MD) approach that allows for tuning of the parameters that contribute to reaction rates.…”

Establishing a Connection for Students between the Reacting System and the Particle Model with Games and Stochastic Simulations of the Arrhenius Equation

“…The same is the case for molecular Monte Carlo simulation (MC) which requires several of the MD methods and in addition the introduction of the Metropolis scheme. Such simulation methods are very useful in education, 1 but usually, they are not meant to teach the basic mathematical understanding, algorithms, and programming addressing chemical problems. Methodically, the approach here goes beyond that and focuses on the development of computer algorithms for simulating the temperature dependence of chemical kinetics with students.…”