Paper

Paper: Nitrogen splitting

Felix

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.

Paper: OpenMolcas – a powerful electronic structure code going open-source

Felix

You can find the new paper describing the OpenMolcas package in JCTC – OpenMolcas: From source code to insight. OpenMolcas represents the open-source release of the previously commercially distributed Molcas package. Use OpenMolcas to gain access to powerful multireference methods for free and to have full control if you need to modify the source.

My own contributions to Molcas are concerned with the implementation of the wavefunction analysis module &WFA , as described in JCTC 13, 5343 (2017), and the interface to Columbus. Let me know if you have any questions about these.

Paper: Details in the surface hopping method

Felix

Our paper “Strong Influence of Decoherence Corrections and Momentum Rescaling in Surface Hopping Dynamics of Transition Metal Complexes” was just accepted in JCTC. In this work we investigated the reliability of the surface hopping method in the case of a transition metal complex described using a linear vibronic coupling model. We found that various seemingly unimportant parameters can have a strong influence on the results.

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Paper: Two-photon absorption

Felix

Our new paper Effect of Symmetric and Asymmetric Substitution on the Optoelectronic Properties of 9,10-Dicyanoanthracene, written in collaboration with colleagues from Imperial College London, TU Vienna, University of Geneva, and the Polish Academy of Sciences just appeared in the new RSC journal Molecular Systems Design & Engineering. The paper illustrates design principles relevant for strong two-photon absorbers. The best two-photon absorption is obtained by using a symmetric D-A-D arrangement with sufficiently strong donors.

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Paper: Electronic structure methods for dynamics simulations

Felix 1 Comment

The challenge about running photodynamics simulations is that the computational cost is often so high that one might have to compromise in terms of the electronic structure method used. One is tempted to just check the vertical excitations at one geometry and run the dynamics if those look alright. How this can go wrong is investigated in the paper “The Influence of the Electronic Structure Method on Intersystem Crossing Dynamics. The Case of Thioformaldehyde” that just appeared in JCTC. Take a look if you are interested.

 

Copyright 2019 American Chemical Society.

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Paper: Delayed fluorescence

Felix

Small modifications can make a big difference. Swapping anthraquinone for a thiophene based acceptor in a donor-acceptor-donor system produces the desired red shift in the emission but limits its quantum efficiency. This conclusion was drawn from a recent paper lead by Stephanie Montanaro and Iain Wright at Loughborough: Red-shifted delayed fluorescence at the expense of photoluminescence quantum efficiency – an intramolecular charge-transfer molecule based on a benzodithiophene-4,8-dione acceptor which just a appeared in PCCP.

Computations reveal that the reason for the reduced emission quantum efficiency lies in the presence of low-lying locally excited states (4 triplets and one singlet) on the central unit.

Paper: Visualisation of electron correlation

Felix

Felix’s first purely Loughborough grown paper just appeared as a Communication in ChemPhotoChem: “Visualisation of Electronic Excited‐State Correlation in Real Space“. The paper explores a new method for visualising electron correlation exemplified in the case excited states represented in the electron/hole picture. The idea is to fix the hole on one fragment of the system and to observe how the excited electron adjusts to this position.

Below, I am showing this analysis for the lowest 10 excited states of the system. The hole (shown in red) is always located on the second thiophene unit from the right. The electron (shown in blue) adjusts in different ways to this hole position, either moving toward it or going away from it.

As shown above, the method offers a new and intuitive way of viewing correlated exciton wavefunctions. It was also shown in this paper how the method allows to naturally distinguish between ionic and covalent states of naphthalene without any explicit reference to valence bond theory.

Paper: Two-Photon Polymerisation Initiators

Felix

A joint experimental and computational study with groups from Vienna and Geneva just appeared in Sci. Rep.: “Wavelength-optimized Two-Photon Polymerization Using Initiators Based on Multipolar Aminostyryl-1,3,5-triazines.” In this paper, the two-photon absorption properties of a new class of aminostyryl-triazines were investigated showing good agreement between experiment and computation. Furthermore, the practical applicability of these molecules for 3D-printing was shown.

Paper: Dynamics within an Exciton Model

Felix

Another paper working on improving the efficiency of surface hopping dynamics just appeared, this time in JCTC: “Surface hopping within an exciton picture – An electrostatic embedding scheme.” authored by M. F. S. J. Menger, F. Plasser, B. Mennucci, and L. González. In this paper, we explored the possibility of running nonadiabatic dynamics simulations within an exciton model. The main challenge in this endeavour was to derive a consistent energy expression for combining QM/MM electrostatic embedding calculations of the different chromophores.

Surface Hopping within an Exciton Scheme

To test the implementation, we ran simulations on a molecular dyad, where full TDDFT nonadiabatic dynamics simulations were available. Good agreement was found.

The method was implemented in the SHARC molecular dynamics package.