New excited state methods for overcoming challenges in sunlight conversion

Introduction

The dynamics of charges and atoms when electrons are excited to energy levels above the ground state underpins energy conversion in photosynthesis, photocatalysis, and solar cell technologies. Modelling excited electronic states remains, however, a major challenge.

Challenges in Modelling Excited States

While density functional theory (DFT) has been hugely successful in predicting ground state properties of systems with several atoms and electrons, excited state extensions based on time-dependent formulations often lack the required accuracy. I have pioneered alternative approaches where the excited state orbitals are variationally optimized by converging on saddle points on the electronic energy surface.

Preliminary Findings

Preliminary studies show that such time-independent methods have similar efficiency and predictive power as ground state DFT. The central idea of NEXUS is to develop an innovative computational framework leveraging saddle point search strategies to significantly expand excited state simulations beyond their current scope.

Validation through Modern Techniques

Meanwhile, modern ultrafast X-ray techniques can achieve structural sensitivity for organic chromophores, offering a means to validate and complement the theoretical models for this important class of photoactive systems.

Goals of NEXUS

By simulating the excited states in condensed phase rather than gas phase and directly visualizing atomic motion via ultrafast X-rays, NEXUS will provide unprecedented insights into the electronic and structural dynamics of organic molecules with applications in:

1. Photoswitching
2. Singlet fission
3. Artificial photosynthesis

The goal is to unravel the elusive interplay between structure and function and pave the way to the rational design of photofunctional systems, enhancing the efficiency of solar energy conversion.

Broader Impact

An effective, low-cost approach for modelling excited states of large systems is groundbreaking and will have an impact well beyond organic molecules, enabling the study of charge and atom dynamics in photochemical reactions for a wide range of applications.