Wavefunction analysis

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 3.1.1 (23 June 2023)

Size: 12 MB
Version: 3.1.1
Download3549 Downloads

Full release notes

Continue reading →

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

Delayed fluorescence

Felix

Patrick’s first paper as first author just appeared in PCCP: The role of excited-state character, structural relaxation, and symmetry breaking in enabling delayed fluorescence activity in push-pull chromophores. Well done Patrick!

We were interested in understanding the difference in thermally activated delayed fluorescence (TADF) between two closely related donor-acceptor-donor systems using either an anthraquinone and benzodithiophenedione acceptor units, respectively. The first one was known to be an effective TADF emitter [JACS 2014, 136, 18070] whereas the second one had significantly lower quantum yield for TADF [PCCP 2019, 21, 10580].

Rather than just presenting energies, it was the purpose of this paper to shed detailed insight into the wavefunctions involved. Notable differences in the wavefunctions and charge-transfer character were found between the two molecules. Even more striking differences existed between different computational methods.

After evaluating electronic structure methods, we presented geometry optimisations in solution, highlighting the importance of symmetry breaking for producing an emissive lowest singlet state. The role of different solvation models was discussed as well.