Properties of Local Electronic Structures

The simulation of intrinsic contributions to molecular properties holds the potential to allow for chemistry to be directly inferred from changes to electronic structures at the atomic level. In the present study, we demonstrate how such local properties can be readily derived from suitable molecular orbitals to yield effective fingerprints of various types of atoms in organic molecules. In contrast, corresponding inferences from schemes that instead make use of individual atomic orbitals for this purpose are generally found to fail in expressing much uniqueness in atomic environments. By further studying the extent to which entire chemical reactions may be decomposed into meaningful and continuously evolving atomic contributions, schemes based on molecular rather than atomic orbitals are once again found to be the more consistent, even allowing for intricate differences between seemingly uniform nucleophilic substitutions to be probed.Comment: 20+6 pages, 7 figures. SI as an ancillary fil

Decomposing Chemical Space: Applications to the Machine Learning of Atomic Energies

We apply a number of atomic decomposition schemes across the standard QM7 dataset -- a small model set of organic molecules at equilibrium geometry -- to inspect the possible emergence of trends among contributions to atomization energies from distinct elements embedded within molecules. Specifically, a recent decomposition scheme of ours based on spatially localized molecular orbitals is compared to alternatives that instead partition molecular energies on account of which nuclei individual atomic orbitals are centred on. We find these partitioning schemes to expose the composition of chemical compound space in very dissimilar ways in terms of the grouping, binning, and heterogeneity of discrete atomic contributions, e.g., those associated with hydrogens bonded to different heavy atoms. Furthermore, unphysical dependencies on the one-electron basis set are found for some, but not all of these schemes. The relevance and importance of these compositional factors for training tailored neural network models based on atomic energies are next assessed. We identify both limitations and possible advantages with respect to contemporary machine learning models and discuss the design of potential counterparts based on atoms and the intrinsic energies of these as the principal decomposition units.Comment: 21+7 pages, 6 figures. SI as an ancillary file. Version 2: All PhysNet-based results are now based on NN models trained on a combination of atomic and molecular energies (as opposed to only the former in Version 1). SI also updated with a total of four figure

QM7 Decomposed Data

This data is in support of our article 'Decomposing Chemical Space: Applications to the Machine Learning of Atomic Energies' (arXiv:2212.09489). An example python script is provided with more details about the PySCF and DECODENSE settings. DATA The data is saved in Numpy .npz format. The files are named as b3lyp_{basis_set}_qm7_{decomposition}_atomization.npz The keys in each file correspond to: 'mol_idx': Molecule index corresponding to the molecule index in original QM7 dataset. 'N' : Number of atoms in the molecule 'Z' : Nuclear charges 'R' : Coordinates (ångstrom) 'E' : Total atomization energy (kcal/mol) 'Ea' : Atomization energy per atom (kcal/mol

Dihydroazulene‐Azobenzene‐Dihydroazulene Triad Photoswitches

Photoswitch triads comprised of two dihydroazulene (DHA) units in conjugation to a central trans-azobenzene (AZB) unit were prepared in stepwise protocols starting from meta- and paradisubstituted azobenzenes. The para-connected triad had significantly altered optical properties and lacked the photoactivity of the separate photochromes. Instead, for the meta-connected triad all three photochromes could be photoisomerized to generate an isomer with two vinylheptafulvene (VHF) units and a cis-azobenzene unit. The photoisomerizations were studied by ultrafast spectroscopy, revealing a fast DHA-to-VHF photoisomerization and a slower trans-to-cis AZB photoisomerization. This meta triad underwent thermal VHF-to-DHA back-conversions with a similar rate of all VHFs, independent of the identity of the neighboring units, and in parallel thermal cis-to-trans AZB conversion. The experimental observations were supported by computations (excitation spectra and orbital analysis of the transitions)