Molecular Dynamics

Molecular dynamics (MD) is a powerful tool for describing individual interactions between particles (atoms and molecules in gases, plasma, and solids).  The centerpiece of any MD-based approach is the potential energy surface (PES) – a function of several variables that gives the forces acting between a pair of atoms. Design of PESs is a multidisciplinary problem itself, making the MD approach a cutting-edge discipline. Having in hands a PES of interest, one can obtain an unprecedented detalization of processes taking place in nature.

In the HTGD, we apply MD methods to study molecular processes in hot air – i.e. in the flow heated by shock waves around flying objects. This research is of interest to DOD, AFOSR, and NASA.

This movie shows the complexity of an actual underlying collisional dynamics in atmospheric species (such as O2 and N2). These mutual “vibrations” and internal energy “scrambling” are due to specifics in the electronic shells of molecular species. The collisional dynamics reflects on the micro- and macroscopic properties of the flow.

For example, we know that ozone (O3) is an important species in the Earth atmosphere which shields us from the harmful UV radiation. Turns out, the reactivity of O2-O collisions produces an unusual behavior of the O2 vibrational mode when it is driven out of equilibrium. It is conventionally assumed that vibrational relaxation becomes more efficient with increasing temperature, however, in the case of O2-O, the trend is opposite. Due to the absence of potential barrier at the O2-O approach, vibrational relaxation in such collision is most efficient at room temperatures while at hypersonic conditions, in the abundance of atomic oxygen, such collisions are less likely to induce an event of vibrational energy transfer.

On the macroscopic level, the state-of-the-art calculations show discrepancies between experimental measurements and theoretical predictions produced by conventional models. The differences are observed in the heat flux and pressure, two critical parameters for the design of a spacecraft. In HTGD lab we develop high fidelity models of chemically reacting flows from first principles, i.e. via propagating trajectories of individual particles and gathering statistical data and coupling it with the state-of-the-art CFD methods.