Accurate simulations of photochemical and photophysical processes at materials interfaces

Introduction

The PhotoMat project will develop highly accurate methods for the prediction of excited-state properties and dynamics of materials interfaces based on ab initio Green's function theory in the GW approximation. Insight into the intricate processes unfolding after photoexcitation is crucial to realizing the vision of ‘materials by design’.

Theoretical Framework

A detailed understanding of experiment requires aid from theory. However, currently there is no computational method available that can provide reliable excited-state nuclear forces for materials. I propose here to advance the GW-Bethe-Salpeter equation formalism (BSE@GW), which is computationally very expensive.

Methodology

While GW is considered the gold standard for the computation of band structures, the BSE@GW scheme is the method of choice for describing the formation of excitons (bound electron-hole pairs) in materials. I recently contributed to pushing GW to system sizes of up to 1000 atoms, often required to model materials interfaces.

Overcoming Limitations

I will leverage these advancements to overcome the restriction of BSE@GW to small systems, enabling calculations of similar size. This will be achieved by:

1. Reducing the scaling of the BSE step with respect to system size.
2. Implementing efficient periodic boundary conditions.
3. Optimizing the algorithm for execution on the emerging generation of exascale supercomputers.

Excited-State Dynamics

Excited-state geometry optimization will be enabled by implementing accurate analytic nuclear BSE forces. Non-adiabatic molecular dynamics will be unlocked by combining the low-scaling BSE energies and forces with surface hopping schemes and machine learning potentials.

Applications

I will employ the newly developed methods to investigate promising candidates for tailored photonic devices. This will include the study of:

• Photoisomerization reactions at 2D materials.
• The formation of charge-transfer excitons in moiré structures.

Conclusion

PhotoMat is here the crucial link that bridges the divide between theory and experiment.