Disentanglement of triplet and singlet states of azobenzene: direct EELS detection and QMC modeling

Abstract

Singlet and triplet excited states of trans-azobenzene have been measured in the gas phase by electron energy loss spectroscopy (EELS). In order to interpret the strongly overlapping singlet and triplet bands in the spectra a set of large-scale correlated quantum Monte-Carlo (QMC) simulations was performed. The EELS/QMC combination of methods yields an excellent agreement between theory and experiment and for the two low-lying excited singlet and two low-lying triplet states permitted their unambiguous assignment. In addition, EELS revealed two overlapping electronic states in the band commonly assigned as S(2), the lower one with a pronounced vibrational structure, the upper one structureless. Finally, the agreement between theory and experiment was shown to further increase by taking computationally into account the finite temperature effects.

Rigidity of the conductance of an anchored dithioazobenzene optomechanical switch

“…Our present study as well as our recent many-body study of the AB molecule [53,54] do not support reason a). The many-body study revealed deviations from experiments by as much as ≈1 eV with DFT techniques and even with medium-quality quantum chemistry methods [53,54], depending on the level of correlation and/or basis set used.…”

“…Our present study as well as our recent many-body study of the AB molecule [53,54] do not support reason a). The many-body study revealed deviations from experiments by as much as ≈1 eV with DFT techniques and even with medium-quality quantum chemistry methods [53,54], depending on the level of correlation and/or basis set used. However, these differences affect mostly the singlet/triplet excited states of the molecule [54], rather than the states around the Fermi level responsible for the conductance of the contacted molecule which are very similar for both isomers.…”

“…The many-body study revealed deviations from experiments by as much as ≈1 eV with DFT techniques and even with medium-quality quantum chemistry methods [53,54], depending on the level of correlation and/or basis set used. However, these differences affect mostly the singlet/triplet excited states of the molecule [54], rather than the states around the Fermi level responsible for the conductance of the contacted molecule which are very similar for both isomers. Reason b) is also not supported by our study as the Fermi level is pinned to the tail of the HOMO in all the systems studied.…”

Quantum Monte Carlo for noncovalent interactions: an efficient protocol attaining benchmark accuracy

“…Indeed, this has to be done in a stepwise manner since several sets of parameters enter the multistage approach 37,38 : Table 1 The FN-DMC interaction energies E (kcal/mol) obtained from various tested protocols compared to the CCSD(T)/CBS reference E R (kcal/mol). The protocol-type attribute, if applicable, is indicated in the column P. For clarity, analyzed features of the protocols with respect to the standard 26 3tJ protocol are indicated by the bold typeface.…”

Electron collisions with molecules and molecular clusters

“…Electron scattering experiments allow an insight into, for example, the electronic structure of molecules (e.g. [2]) as well as enabling the investigation of more fundamental phenomena like quantum coherence [3] and others [4]. From an applied perspective, the requirement to quantify and understand electron-molecule collisions stems from a number of fields and media [5,6]: from astrophysics to both natural and man-made plasmas (used, for example, in industry for microchip production) and processes induced by secondary electrons generated by ionizing radiation incident on biological (e.g.…”