Wavefunction analysis

Rationalising Exciton Interactions in Aggregates

Felix

Understanding exciton interactions via a dipole model is often not very intuitive and, more importantly, a dipole model cannot explain the short-range interactions that are often crucial in determining interchromophore interactions.

In our new article [1], exciton coupling in organic chromophores is revisited through the lens of the transition density. The presented formalism gives insight into the strength and sign of the coupling based on the relative arrangement of the lobes of the transition density explaining oscillations between H- and J-aggregate behavior observed when two molecules are displaced relative to each other.

[1] J. Krieger, F. Plasser: Rationalising Exciton Interactions in Aggregates Based on the Transition Density, Chem. Eur. J. 2025, DOI: 10.1002/chem.202501570.

De-excitations

Felix

F. Plasser, On the Meaning of De-Excitations in Time-Dependent Density Functional Theory Computations, J. Comp. Chem. 2025, 46, e70072

De-excitations play a central role in the mathematical formalism of time-dependent density functional theory, but their physical meaning has not been studied in detail. This work sheds new light onto this issue by showing that de-excitations arise naturally also in wave function based theories where they represent ground-state correlation.

Ionic states

Felix

Our new paper Quantification of the Ionic Character of Multiconfigurational Wave Functions: The Qat Diagnostic just appeared in the Journal of Physical Chemistry A.

The paper deals with the fact that the widely used CASSCF method, if not used carefully, can yield large errors (1-2 eV) in vertical excitation energies. This problem arises for ionic states, as defined within valence bond theory. Within this work we developed a simple diagnostic to identify ionic states. We found a good correlation between the new diagnostic (Qta) and the error, as shown in the figure above.

We hope that the new diagnostic will be useful similar to analogous diagnostics identifying charge transfer states in TDDFT computations. This will give users the possibility to spot potential problems quickly.

On-going work is concerned with going from just diagnosing the problem to developing a numerical correction term to fix the problem.

HOMO/LUMO transitions

Felix

We just posted a preprint discussing a question I have been wondering about for a while: Why is the lowest excited state of a molecule not always the HOMO/LUMO transition? More generally we show how singlet and triplet state energies are affected in different ways by post-MO energy terms.

The preprint can be found here: Excited-state energy component analysis for molecules – Why the lowest excited state is not always the HOMO-LUMO transition

Update: the final published version is available here.

Classification and Analysis of Excited States

Felix

A new book chapter by Patrick and Felix just appeared online: “Classification and Analysis of Molecular Excited States“. Ultimately, this chapter will be part of the Comprehensive Computational Chemistry series published by Elsevier.

In this chapter we explore the various ways in which excited states are classified, that is, according to

  • the molecular orbitals involved,
  • valence bond resonance structures,
  • spatial and spin symmetry,
  • more fundamental wavefunction properties (double excitations, correlation, etc),
  • excited-state aromaticity, and
  • delocalisation and charge transfer.

The map below shows the different classes and highlights the multitude of ways that are used to discuss excited states in the literature.

It is the purpose of this chapter to discuss all these types of states, covering the mathematical and physical background as well as the consequences to spectroscopy and photochemistry.

Doubly excited states

Felix

Our new paper “Classification of Doubly Excited Molecular Electronic States” just appeared in Chemical Science.

The topic of doubly excited states has been discussed quite controversially in the literature over the last couple of years, see for example JACS, 139, 13770 (2017) and JCTC 14, 9 (2018), and it is often disputed whether to classify a state as doubly excited at all. To contribute to this discussion we worked on the development of a physically motivated definition of doubly excited character based on operator expectation values and density matrices, which works independently of the underlying orbital representation. We hope that this approach will provide new understanding on these issues.

Release of TheoDORE 3.0

Felix

Version 3.0 of the TheoDORE wavefunction analysis package is available. Download the current version below.

New features of TheoDORE 3.0

  • New user interface and documentation
  • Improvement for VIST (plot_vist)
  • Improvements for natural orbital analysis (analyze_nos) including unrestricted orbitals
  • LOC for ionic states (analyze_tden)
  • Jmol densities (jmol_mos)
  • State-to-state TDM
  • Updated ADF interface
  • ONETEP interface
  • Excitation number, modified from [DOI: (10.1021/acs.jctc.7b00963)]

Note: TheoDORE 3 has a modified user interface. To use TheoDORE call

theodore theoinp

theodore analyze_tden

theodore analyze_nos

etc.

TheoDORE – Download

Download the newest release of the TheoDORE wavefunction analysis program – TheoDORE 3.2 (22 July 2024)

Size: 12 MB
Version: 3.2
Download4293 Downloads

Full release notes

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libwfa: Wavefunction analysis tools

Felix

Our new paper “libwfa: Wavefunction analysis tools for excited and open-shell electronic states” was just published in WiRES Comp. Mol. Sci. The libwfa library provides a variety of visual and qunantitative analysis tools to post-process excited-state computations performed within Q-Chem and OpenMolcas.

You can find the libwfa functionality in the Q-Chem documentation under General Excited-State Analysis. To activate libwfa in Q-Chem, use

state_analysis = true

In OpenMolcas use the WFA module, activated via

&WFA