arXiv subjects

Elli Selenius

Publications and source records attributed to Elli Selenius.

3 recordsLinked to original sources

arXiv2026

Orbital-optimized density functional calculations of excited electronic states: Recent advances and perspectives

Orbital-optimized (OO) density functional calculations provide a time-independent, variational route to electronic excitations, alternative to presently widely used time-dependent density functional theory (TDDFT) approaches. As the orbitals are optimized in a state specific way, these methods can provide a balanced description of excited states with different character, thereby overcoming several limitations of practical implementations of TDDFT. Driven by recent developments in algorithms for obtaining excited states as saddle points on the electronic energy surface, OO methods have attracted increasing interest, maturing into an active and rapidly expanding area of research. Here, the theoretical foundations of the approach are clarified and an overview of recent methodological developments in excited-state orbital optimization is provided. An overview of methods for treating open-shell singlet excited states and current approaches for computing transition properties and spectra is also provided. Finally, recent applications to molecular Rydberg, charge-transfer, and core excitations are reviewed, with the aim of assessing the present accuracy and range of applicability of OO density functional calculations with common exchange and correlation functionals.

physics.chem-ph↗

arXiv2025

Freeze-and-release direct optimization method for variational calculations of excited electronic states

Variational optimization of orbitals in time-independent density functional calculations of excited electronic states presents a significant challenge, as excited states typically correspond to saddle points on the electronic energy landscape. The optimization can be particularly difficult if the excitation involves significant rearrangement of the electron density, as for charge transfer excitations. A simple strategy for variational orbital optimization of excited states is presented. The approach involves minimizing the energy while freezing the orbitals directly involved in the excitation, followed by a fully unconstrained saddle point optimization. Both steps of this freeze-and-release strategy are carried out using direct optimization algorithms with the same computational scaling as ground state calculations. The performance of the method is extensively assessed in calculations of intramolecular and intermolecular charge transfer excited states of organic molecules and molecular dimers using a generalized gradient approximation functional. It is found that the freeze-and-release direct optimization approach can avoid variational collapse to spurious, charge-delocalized solutions for cases where conventional algorithms based on the maximum overlap method fail. For intermolecular charge transfer, the orbital-optimized calculations are found to provide the correct dependency of the energy on the donor-acceptor separation without requiring long-range exact exchange, something common time-dependent density functional theory approaches fail to achieve.

physics.chem-ph↗

arXiv2023

Orbital-optimized versus time-dependent density functional calculations of intramolecular charge transfer excited states

The performance of time-independent, orbital optimized calculations of excited states is assessed with respect to charge transfer excitations in organic molecules in comparison to the linear-response time-dependent density functional theory (TD-DFT) approach. A direct optimization method to converge on saddle points of the electronic energy surface is used to carry out calculations with the local density approximation (LDA) and the generalized gradient approximation (GGA) functionals PBE and BLYP for a set of 27 excitations in 15 molecules. The time-independent approach is fully variational and provides a relaxed excited state electron density from which the extent of charge transfer is quantified. The TD-DFT calculations are generally found to provide larger charge transfer distances compared to the orbital optimized calculations, even when including orbital relaxation effects with the Z-vector method. While the error on the excitation energy relative to theoretical best estimates is found to increase with the extent of charge transfer up to ca. $-2$ eV for TD-DFT, no correlation is observed for the orbital optimized approach. The orbital optimized calculations with the LDA and the GGA functionals provide a mean absolute error of $\sim$0.7 eV, outperforming TD-DFT with both local and global hybrid functionals for excitations with long-range charge transfer character. Orbital optimized calculations with the global hybrid functional B3LYP and the range-separated hybrid functional CAM-B3LYP on a selection of states with short- and long-range charge transfer indicate that inclusion of exact exchange has a small effect on the charge transfer distance, while it significantly improves the excitation energy, with the best performing functional CAM-B3LYP providing an absolute error typically around 0.15 eV.

physics.chem-ph↗