3D visualisation of chemical shielding tensors

Aromaticity is a ubiquitous yet elusive concept in chemistry and chemists have spent a great deal of effort on developing methods to quantify and visualise aromaticity. One particularly popular method is the nucleus independent shift (NICS), which can be seen as a virtual NMR experiment carried out within a conjugated ring to evaluate the enhanced chemical shielding induced by aromatic ring-currents. Strikingly NICS also allows to quantify antiaromaticity, as this induces a net deshielding effect within the ring. NICS provides a powerful quantitative aromaticity criterion but the main challenge for its graphical representation is that the chemical shielding is a 3×3 tensor, which is difficult to visualise with the existing methods.

Therefore, we have developed a new method for the visualisation of chemical shielding tensors (VIST), which provides a local representation of the shielding tensor along with the molecular structure. The method, thus, allows to probe local aromaticity along with the underlying anisotropy of the shielding. The method is described in the preprint “3D Visualisation of chemical shielding tensors to elucidate aromaticity and antiaromaticity” available on ChemRxiv.

Within the preprent we exemplify the main concepts in the benzene and phenanthrene molecules and continue by studying

The underlying code is scheduled to be released within the next version of the TheoDORE wavefunction analysis package.

Release of TheoDORE 2.3.

Version 2.3 of the TheoDORE wavefunction analysis package is available. Download the current version below.

New features of TheoDORE 2.3:

  • Compute (unpaired) densities using orbkit
  • Fix for theo_test.bash
  • Fix for ORCA osc. strengths
  • Old RASSI interface removed (was not working properly)
TheoDORE – Download

Download the newest release of the TheoDORE wavefunction analysis program – TheoDORE 2.3 (18 Nov. 2020)

Size: 12 MB
Version: 2.3

Full release notes:

Continue reading

Release of TheoDORE 2.2

Version 2.2 of the TheoDORE wavefunction analysis package is available. Download the current version below.

New features of TheoDORE 2.2:

  • Support for spin-unrestricted calculations (by Sebastian Mai) – currently only tested for ORCA
  • Substituent-induced electron localization (SIEL) as described in Chem. Sci. 2020, 10.1039/D0SC01684E
TheoDORE – Download

Download the newest release of the TheoDORE wavefunction analysis program – TheoDORE 2.3 (18 Nov. 2020)

Size: 12 MB
Version: 2.3

Full release notes:

Continue reading

Directional excitations in photosensitisers

Characterising excited states in transition metal complexes by looking at pictures of orbitals can be a tedious task. Even more, it is hard to eliminate personal in the process and produce quantitative results. In a study led by Pedro Sánchez-Murcia from the University of Vienna, we have taken a closer look at this problem in the case of various substituted complexes deriving from the archetype Ru(bpy)3 with the aim of quantifying how different substituents influence the localisation of the excited electron. The result is presented in the article “Orbital-free photophysical descriptors to predict directional excitations in metal-based photosensitizers,” which just appeared in Chemical Science.

Paper: TheoDORE electronic structure analysis

The paper TheoDORE: A toolbox for a detailed and automated analysis of electronic excited state computations just appeared in the Journal of Chemical Physics in a special issue on Electronic Structure Software. Please, take a look if you are interested in speeding up the analysis of your excited-state computations. If you are already a user of TheoDORE, you can learn about the latest developments and obtain a compact overview of the underlying theory.

Paper: Nitrogen splitting

Splitting N2 is a challenging undertaking due to the strong triple bond holding the two nitrogen atoms together. Traditionally, this task is achieved via the Haber-Bosch process but recently interest has shifted to the possibilities of nitrogen splitting via homogeneous catalysis. Computations on the dinuclear transition metal complexes involved can be performed thanks to modern computational hardware and appropriate computer codes. However, the analysis of the excited states involved can become a significant challenge due to the large number of states and difficulties in assigning their character unambiguously. To tackle this problem, we have recently devised a strategy for a detailed analysis of the electronic wavefunctions of the states contributing to the reactive process. The associated paper, led by S. Rupp and V. Krewald from TU Darmstadt, just appeared in the European Journal of Inorganic Chemistry: Multi‐tier electronic structure analysis of Sita’s Mo and W complexes capable of thermal or photochemical N2 splitting.

TheoDORE – Tutorial

An updated version of the tutorial for the TheoDORE wavefunction analysis program is ready, thanks to Patrick. The tutorial can be downloaded here:

For the newest version of the code go here:

In the tutorial, we explain the process of creating conditional electron densities for visualising electron correlation (ChemPhotoChem 2019, 3, 702). The figure below shows a comparison between the ionic and covalent singlet and triplet B3u states of naphthalene.

The tutorial also explains the creation of bar graphs for a compact representation of excited-state character (see Coord. Chem. Rev., 2018, 361, 74 and ChemRxiv.11395314). In the picture below, the excited states of an iridium complex are decomposed into metal-to-ligand charge transfer (MLCT), ligand-to-ligand charge transfer (LLCT), and ligand centred (LC) contributions. The lowest six states are all dominated by MLCT character but the presented analysis clearly shows that the first three have enhanced LC character compared to the latter three.

Two Preprints: Wavefunction analysis

Two new preprints dealing with the analysis of excited-state electronic wavefunctions are available from ChemRxiv.

First, a quick summary of the TheoDORE package: TheoDORE: a Toolbox for a Detailed and Automated Analysis of Electronic Excited State Computations.

Second, a more extensive paper exploring how far we can use information from excited-state wavefunction analysis tools to understand excitation energies beyond the molecular orbital picture. The energy of a correlated electron-hole pair is derived using diagrammatic techniques and this information is further used for a graphical depiction in terms of different charge distributions and their electrostatic potentials. Doing so turned out not as easy as hoped for but was very exciting. Find more here: Toward an Understanding of Electronic Excitation Energies Beyond the Molecular Orbital Picture by P. Kimber and F. Plasser.