Unraveling the Electronic Properties of Water: A Breakthrough Study by EPFL Researchers

2024-03-06 08:10:13

Water molecules and electron density corresponding to the exciton state resulting from photon absorption. Credit: Kristian Tambor (background)/Alexi Tal (water molecules)

Researchers at EPFL have achieved a significant breakthrough in understanding the electronic properties of water, a fundamental component of life and the environment.

There is no doubt that names have meaning. Without it, life would never have started, let alone continue today – not to mention its role in the environment itself, with oceans covering over 70% of the Earth.

But despite its ubiquity, liquid water contains some electronic complexities that have long puzzled scientists in chemistry, physics and technology. For example, electron affinity, i.e. the stabilization of the energy a free electron undergoes when trapped in water, remains poorly characterized from an experimental point of view.

Decomposing the electronic properties of water

Even today’s most accurate electronic structure theory has failed to clarify the picture, which means that important physical quantities such as the energy with which electrons from external sources can be introduced into liquid water remain elusive. These properties are essential for understanding the behavior of electrons in water and can play a role in biological systems, environmental cycling and technological applications such as solar energy conversion.

In a recent study, EPFL researchers Alexey Tal, Thomas Bischoff and Alfredo Pasquarello have made significant strides in deciphering the puzzle. Their study, published in PNASRefers to the electronic structure of water using computational methods that go beyond today’s most advanced approaches.

Advanced theoretical approaches

The researchers studied water using a method based on the “many body perturbation theory”. It is a complex mathematical framework used to study the interactions of multiple particles within a system, such as electrons in a solid or molecule, and examines how these particles affect each other’s behavior, not in isolation but as part of a larger, interacting group. Relatively simply, many-body perturbation theory is a way to calculate and predict the properties of a many-particle system by considering all the complex interactions between its components.

But physicists modified the theory with “vertex corrections”: modifications to many-body perturbation theory that account for the complex interactions between particles beyond the simplest approximation. Vertex corrections refine the theory by considering how these interactions affect the energy levels of particles, for example their response to external fields or their self-energy. In short, vertex corrections lead to more accurate predictions of physical properties in a multiparticle system.

Modeling electronic properties of water

Modeling liquid water is particularly challenging. A water molecule contains one oxygen atom and two hydrogen atoms, and both their thermal motion and the quantum nature of their nuclei play a key role. Considering these aspects, the researchers precisely determined the electronic properties of water, such as ionization potential, electron affinity and band gap. These findings are essential for understanding how water interacts with light and other materials at the electronic level.

“Our research on the energy levels of water reconciles high-level theory with experiment,” says Alfredo Pasquarello. Alexey Tal further emphasizes the importance of the new methodology: “Thanks to the advanced description of the electronic structure, we were able to produce an accurate absorption spectrum.”

A new paradigm for material science

The findings have additional implications. The theoretical developments implemented by the EPFL team lay the foundations for a new universally applicable standard for obtaining precise electronic structures of materials. This provides a highly predictive tool that may revolutionize our fundamental understanding of electronic properties in condensed matter science, with applications in the search for material properties with specific electronic functions.