Agenda

"Orbital-optimized density functional calculations of challenging electronic excitations in molecules, molecules in solution, and solids"

Seminar with Dr. Gianluca Levi, winner of an ERC starting grant on the topic "New excited state methods for overcoming challenges in sunlight conversion" ( PE4), at the University of Reykjavik Iceland.

Event organized by professors Maurizio Selva and Stefano Bonetti.

Abstract

Calculating electronic excitations in molecules and condensed-phase systems involved in energy-conversion processes poses significant challenges. The systems are often too big for accurate but computationally costly wave function methods, and the excitations typically involve significant rearrangements of the electron density, which is problematic for affordable time dependent density functional theory (TDDFT) calculations. Time-independent orbital-optimized density functional calculations, where excited states are obtained as saddle points on the electronic energy surface, offer a computationally efficient and accurate alternative. I will present new strategies for excited state orbital optimized calculations. In a first constrained optimization step, where the orbitals involved in the excitation are fixed, the saddle point order of the target excited state is estimated. Thereby, approximate second-order direct optimization algorithms, such as a generalized mode following approach, are used to converge on target saddle points. This novel method shows significant improvements in density functional calculations of charge transfer and Rydberg excited states of molecules, outperforming TDDFT. The method has also been applied in multiscale molecular dynamics simulations of photoexcited metal complexes in solution. Calculations of the long-debate excitations of the charged nitrogen-vacancy center in diamond yield results in close agreement with high-level many-body calculations.

References [1] E. Selenius, A. E. Sigurdarson, Y. L. A. Schmerwitz and G. Levi, J. Chem. Theory Comput., 20, 3809–3822 (2024). DOI: 10.1021/acs.jctc.3c01319.

[2] Y. L. A. Schmerwitz, G. Levi and H. Jónsson, J. Chem. Theory Comput., 19, 3634–3651 (2023). DOI: 10.1021/acs.jctc.3c00178.

[3] A. E. Sigurdarson, Y. L. A. Schmerwitz, D. K. V. Tveiten, G. Levi and H. Jónsson, J. Chem.

Phys., 159, 214109 (2023). DOI: 10.1063/5.0179271.

[4] T. Katayama et al., Chem. Sci., 14, 572–2584 (2023). DOI: 10.1039/d2sc06600a.

[5] A. V. Ivanov, Y. L. A. Schmerwitz, G. Levi and H. Jónsson, SciPost Phys., 15, 1–21 (2023). DOI: 10.21468/SciPostPhys.15.1.009.

It is possible to participate remotely: instructions in the attached poster.