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We study computationally the electronic spectra of C60 thin films using the recently developed density functional theory (DFT) framework combining a screened range separated hybrid (SRSH) functional with a polarizable continuum model (PCM). The SRSH-PCM approach achieves excellent correspondence between the frontier orbital's energy levels and the ionization potential and electron affinity of the molecular system at the condensed phase and consequently leads to high quality electronic excitation energies when used in time-dependent DFT calculations. Our calculated excited states reproduce the experimentally main reported spectral peaks at the 3.6-4.6 eV energy range and when addressing excitonic effects also reproduce the red-shifted spectral feature. Notably, we analyze the low-lying peak at 2.7 eV and associate it to an excitonic state.

The low energy excited states of the conformational isomers of solvated azobenzene are calculated with several DFT methods accounting for the solute-solvent interaction implicitly with the polarizable continuum model or explicitly with subsystem DFT. For the latter, embedding potentials are calculated for 21 sampled snapshots of the solvent molecules. First, we find that accounting for the solvent implicitly or explicitly has little effect on the predicted cis-trans S1 excitation energy gap. Second, we find that azobenzene's S1 cis and trans energies are accurate as long as a screened range-separated hybrid exchange-correlation functional is employed. Finally, we also tested a simplified workflow whereby a single, averaged, embedding potential is used. Unfortunately, we find larger deviations against the experiment for the simplified workflow. This highlights a basic flaw in the approach, where the time scale of solvent averaging is much longer than that of the solute's electronic polarization. © 2022 American Chemical Society.

On the basis of first-principle calculations, we have studied the electronic and magnetic properties of a series of one-dimensional metal–organic frameworks (MOFs), labeled as MIT. These are coordi...

We study computationally the electronic spectra of C

Presently, great attention is focused on the search for promising anode materials due to the rapid development of electronic products. In this study, by means of density functional calculations, we...

Electrocatalytic water spliting is the most attractive route for hydrogen production, but the development of nonprecious, stable, and high-performance catalysts for hydrogen evolution reaction (HER) to replace the scarce platinum group metal-based electrocatalysts is still a challenging task for the scientific community. In this work, within the framework of density functional theory computations, we have predicted that a silicon and phosphorus co-doped bipyridine-linked covalent triazine framework, followed by substitution of bipyridine hydrogens at the P-site with fluorine atoms, may be a potential catalyst for HER. Our predicted model system (SiPF-Bpy-CTF) exhibits a very low band gap (7 meV), which may exhibit facile charge transfer kinetics during HER. Using the Gibbs free energy for the adsorption of atomic hydrogen ([Formula: see text]) as the key descriptor, we have found that our proposed model system (SiPF-Bpy-CTF) exhibits superior HER catalytic activity, with its [Formula: see text] being close to the ideal value (0 eV).

By using a state-of-the-art theoretical method, we have investigated the electronic structure of a new class of nanocomposites, namely, porous graphene (PG)–fullerene (PG–fullerene) composite. We have utilized the porosity of PG to encapsulate the fullerene molecule into it and have investigated the efficacy of the PG–fullerene composite in solar cell and optoelectronic applications. Our study reveals that smaller sized composites show type-II band alignment, suggesting efficient charge separation upon photoexcitation. Hence, these composites may be utilized for designing solar cells. However, larger composites show type-I band alignment, thereby limiting their applications in solar cell. We further propose graphene antidot–fullerene composites with same pore structure as that of PG, which show type-II band alignment even for larger antidots. Qualitative analysis reveals that the electron injection rate as well as charge separation capability of antidot composites is larger than that of the PG composites....

By using the state-of-the-art theoretical method, we have investigated the electronic structures of recently synthesized two-dimensional azine-linked covalent organic framework (ACOF-1). Our result indicates that ACOF-1 is a direct band gap semiconductor, suggesting useful application in nanoelectronics. Its one-dimensional (1D) structure also exhibits semiconducting properties. Furthermore, this azine-linked COF is found to be practically useful for selective sensing of nitroaromatics over nitroaliphatics. Lastly, our calculations reveal a more realizable way for using two tautomers of ATFG-COF, a derivative of ACOF-1, in conductance switching device by means of transport property calculation. Therefore, our present study may provide a guideline for multifunctionalities of azine-linked COF (ACOF-1).

By using first principle calculations we have studied the magnetic, electronic and transport properties of zigzag-graphene nanoribbon (zGNR) with a topological line defect (LD) composed of pentagons and heptagons (5-7). We show that one can engineer the magnetic and electronic properties of the edge passivated zGNR with 5-7 LD through the variation of either the width of the zGNR or the position of the LD. Thus, one can have ferromagnetic behaviour in zGNR by introducing 5-7 LD close to one edge of the ribbon. One can tune the zGNR with 5-7 LD from semi-metallic to semi-metallic semiconductor either by increasing the width of the ribbon or by changing the position of the LD. We have also studied the effect of the doping on the degeneracy of the spin states of 4-4-LD-zGNR. The calculation of transport properties of N-doped 4-4-LD-zGNR reveals that it has high spin filtering efficiencies. The tuning of the spin polarization through the formation of 5-7 LD in zGNR holds a promise for its application in spintronic devices.

Inspired by recent experimental synthesis of two-dimensional cobalt bis(dithioline) (CoBHT) metal–organic surface (J. Am. Chem. Soc., 2015, 137, 118–121), herein, using first principle calculations, we have investigated the electronic and magnetic properties of two-dimensional BHT-based metal (M = Co, Fe, Mn, Cr)-organic frameworks (MBHT). Our detailed theoretical calculations predict that CoBHT, FeBHT, and MnBHT are planar ferromagnetic (FM) half-metals, whereas CrBHT is planar spin-frustrated kagome lattice antiferromagnetic (AFM) semimetal, a new state of matter referred as spin-liquid. These planar ferromagnetic half-metal materials are promising candidates for spintronic devices. Further, polluting gas such as CO can be detected by these MOFs as there is remarkable variation of electronic and magnetic properties after gas adsorption. Interestingly, these properties have been found to be a function of coordination environment of central metal atom, which is actually a coordinatively unsaturated (CUS) ...

By using density-functional tight-binding method we have calculated the electronic structure of graphene quantum dot (GQD)-fullerene hybrid systems and explored the efficacy of their use in designing solar cells. We have shown that the electronic energy levels of the nanohybrids can be tuned either by varying the size of the quantum dots or by proper functionalization of the quantum dot (QD). The GQD-fullerene nanohybrids form type-I or type-II band energy alignment depending upon the size of the GQD. Thus, hybrid systems with smaller sized QDs form type-II band energy alignment while those of larger GQDs form type-I alignment. The type-II band alignment confirms the spatial charge separation for the systems and thus the rate of recombination of charge carriers will be low. The value of ΔG i.e. the difference in energy between the LUMO of the donor (GQD) and LUMO of the acceptor (fullerene) which measures the rate of electron injection from the donor to the acceptor is also large for the nanohybrids with smaller GQDs. So, we suggest that GQD-fullerene nanocomposites with smaller GQD will be a suitable system for photovoltaic devices. We also show that the type-II band energy alignment for the nanohybrids with larger QDs can be achieved through the functionalization of the GQD with electron donating group such as -NH2.

With the help of first-principle calculations we have proposed a new 2D metal-organic framework (MOF) consisting of a -NH substituted coronene molecule and transition metals. Our study reveals that formation of such crystals is exothermic in nature, i.e. it is an energetically favourable process. The mode of magnetic coupling between the local magnetic moments and hence the overall magnetic moment of the MOF can be tuned by changing the transition metal. Not only the magnetic properties, but also the electronic structure of the MOF can be regulated from half-metal to spin-semiconductor to semimetallic-semiconductor by altering the metal center from Cr to Mn to Fe/Co. Our study also indicates that the change in the ligand structure and its anchoring group is also very effective in tuning the electronic properties of MOFs. The study of transport properties reveals that the half-metallic crystal possesses the maximum value of the spin-filtering efficiency, i.e. 100%.