Nandini Ananth, Chemistry and Chemical Biology, is a designer. Not of fashion, nor of interiors, but of molecules. Instead of creating a red-carpet gown or a luxe new dining room, Ananth conceives brand-new, ideal materials from the atoms-up, with ideal properties for making our lives easier. These theoretical designs provide blueprints for other scientists so they can synthesize new materials in the lab.
While that day is still a long way off, Ananth is taking the first steps toward making it a reality. “If I build my theories well enough, I could run a simple computer simulation and hand someone a blueprint for a material with the properties they seek,” she says. “That’s a really neat goal and very exciting. Of course we know it’s very difficult to do this—chemistry in real life has so many moving parts, it’s a very difficult process to model.”
Using High-Performance Computing to Tinker with Atoms
Ananth and her team, however, seem up to the challenge. Using theoretical chemistry, they want to better understand the ways in which they can control and direct energy and charge transfer on an atomic level. Tinkering with how an electron jumps from one atom to another has a host of exciting possibilities and promising applications. Ananth and her team first explore the mathematical and quantum mechanical theory behind these phenomena, then use computer programming—often writing their own code—to carry out their problem-solving. “We use high-performance computer clusters to translate our theories into simulations of chemical processes,” she says. Once simulation is successful, the next step is to work with synthetic chemists to make these perfected molecules that can be put to practical uses—such as for harnessing renewable energy.
She explains that modeling how an electron “hops from one atom or molecule to another,” and understanding that behavior on an atomic level, could enable the discovery of a material that can efficiently split water to create fuel. Ananth says the ideal material would be a photo-catalyst that could be thrown into a bucket of water and efficiently split the molecules into hydrogen and oxygen atoms using only sunlight. Unfortunately, current catalysts that split water molecules degrade after the first few water-splitting reactions.
Ananth wants to design a catalyst with more stamina out of a cheap and abundant metal—tweaking something like copper or iron complexes to effectively handle the necessary electron handoff to split water. She points out that with a computer she can do things that can never be done in a lab, which allows for all kinds of tinkering and modifications to the catalyst design. “We can learn from our theoretical tests and make predictions that are realistic,” says Ananth. “And we can identify the correct ‘knobs’ to control these processes.”
Photovoltaics, Solar Cell Materials
This kind of "knob-tweaking" is also promising for developing new types of solar cell materials (known as photovoltaics). Scientists in this field have been on the hunt for good candidates for organic photovoltaics, which are cheaper, biodegradable, and don’t rely on heavy metals (unlike their inorganic counterparts). Unfortunately, all current organic photovoltaics are highly inefficient compared with their inorganic cousins. “An effective organic photovoltaic would be a technological breakthrough,” says Ananth, “so people are thinking about creative ways to enhance their efficiency.”
“I want to design molecules that have an electronic structure that favors singlet fission,” says Ananth. She and her lab, collaborating with Roald Hoffmann, are doing this.
Ananth is looking into a work-around in a phenomenon known as singlet fission: in some materials, absorption of a photon will lead to two excited electrons instead of one, thus doubling the electrical current generated by light absorption. “I want to design molecules that have an electronic structure that favors singlet fission,” says Ananth. She and her lab, collaborating with Roald Hoffmann, Chemistry and Chemical Biology, are doing this while also working with synthesis lab groups to see if the molecules can be made. She hopes to establish a dynamic back-and-forth with these experimental groups, who can report on how the theory plays out in practice and what "knobs" need to be tweaked next in the simulation.
A Chemical Reaction on a Metal Surface
Ananth’s lab also examines what happens when a chemical reaction occurs on a metal surface. Recently, researchers found that the energy released from such reactions can actually dissipate by exciting electrons, rather than simply dissipating through vibrations of the metal lattice, as was previously assumed. The reaction’s heat excites electrons on the metal surface, which in turn can jump to a semiconductor material. “As a mechanism for energy dissipation, it’s a bizarre phenomenon,” says Ananth. “It wasn’t what people were expecting.” The discovery has Ananth and others excited and perplexed, and she’s eager to learn exactly how the electrons are excited, and how this phenomenon may be harnessed for practical use.
After all, as much as Ananth enjoys the abstract theoretical work, she wants to “show how our theories can have significant scientific and societal impact,” she explains. “By expanding the realms of the scientifically possible, theory becomes practically meaningful.”