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Quantum molecular dynamics

The key to problems we didn’t know we had...

One area that is benefitting from supercomputing is quantum molecular dynamics (QMD). Fifty years ago, the concept of being able to model how a collection of molecular systems interact would have been unthinkable. But over time, processing power on desktop systems has increased to the point where calculations that required supercomputers 50 years ago can now be carried out on desktop systems. Some computational chemists have turned the problem round, and instead ask what new science can be made possible by supercomputers, which is where QMD comes in.

In addition to modeling molecules in a computer, it’s now possible to figure out what’s happening to the quantum state of electrons as they move about when two colliding molecules react. Previously, molecular dynamics simulations treated molecules as mechanical models. This gives predictions and answers that are ‘roughly right’, but it has sometimes failed to explain certain phenomena. In particular aspects of biological photosynthesis, for example, computational biochemists have postulated that quantum effects such as tunneling may occur. Tunneling makes use of particles’ dual quantum nature as both solid entities and waves to allow particles like electrons to jump distances that should be too far for them to jump.

Like their colleagues working on climate and weather modeling, or their other colleagues working in cosmology, computational chemists can do ensemble calculations involving lots of simultaneous solutions to work out the statistical likelihood of a proposed chemical reaction mechanism. This has also helped scientists to overturn long-held preconceptions of how reactions work. Understanding exactly how reactions work is crucial, because it will ultimately allow material scientists and chemists to design nanotechnologies and metamaterials, which are materials with properties ‘engineered-in’ at the nanoscales, to help solve humanity’s problems for years to come.