2 research outputs found
Helical and Nonhelical Structures of Vinylene- and Azomethine-Linked Heterocyclic Oligomers: A Computational Study of Conformation-Dependent Optoelectronic Properties
A systematic
computational investigation has been carried out at
the density functional level of theory to characterize various conformational
isomers of furan, pyrrole, and thiophene based oligomers and consequently
study their stabilities and electronic properties, especially in the
cases of long oligomers. In these oligomers, adjacent heterocyclic
rings are connected by either vinylene or azomethine linkages. B3LYP
and B3LYP-D3 functionals are used to observe the effect of dispersion
energy. Our results show that a combination of the B3LYP-D3 functional
and the 6-31GÂ(d,p) basis set is suitable for ground-state studies
of these systems. For long vinylene-linked oligomers, folding isomers
are comparatively more stable than their respective linearly conjugated
isomers, due to intramolecular noncovalent interactions. In the case
of azomethine-linked oligomers, geometries and stabilities of conformers
depend on the type of heterocyclic ring in the repeating unit. For
vinylene-linked heterocyclic oligomers, first optically allowed electronic
transitions of linearly conjugated oligomers have the largest oscillator
strengths, and these absorption bands are dominated by HOMO to LUMO
transitions. In the case of a few linear azomethine-linked oligomers,
two major electronic transitions, S<sub>0</sub> → S<sub>1</sub> and S<sub>0</sub> →S<sub>2</sub>, are noticed. However, transitions
from S<sub>0</sub> to higher electronic states are the most prominent
transitions in cases of foldamers, except azomethine-linked thiophene
foldamers. Major absorption bands of these helical oligomers are dominated
by transitions from HOMO–<i>N</i> to LUMO+<i>N</i> orbitals. All the helical conformers are found to be circular
dichroism active
Informatics-Driven Design of Superhard B–C–O Compounds
Materials containing
B, C, and O, due to the advantages of forming
strong covalent bonds, may lead to materials that are superhard, i.e.,
those with a Vicker’s hardness larger than 40 GPa. However,
the exploration of this vast chemical, compositional, and configurational
space is nontrivial. Here, we leverage a combination of machine learning
(ML) and first-principles calculations to enable and accelerate such
a targeted search. The ML models first screen for potentially superhard
B–C–O compositions from a large hypothetical B–C–O
candidate space. Atomic-level structure search using density functional
theory (DFT) within those identified compositions, followed by further
detailed analyses, unravels on four potentially superhard B–C–O
phases exhibiting thermodynamic, mechanical, and dynamic stability