Unraveling the subtle role of molecular interactions controlling the rheological and thermomechanical responses of graphene-reinforced asphalt binders using molecular dynamics (MD) simulations is a cornerstone problem in statistical thermodynamics because of its chemical heterogeneity, nonergodicity, and sluggish dynamics associated with viscoelastic relaxation. Herein, we emphasize devising generalized models of asphalt binders, resolving finite size effects and phase separation during thermodynamic equilibration of large-scale models, and quantitatively assessing diverse structural and dynamical properties including density, solubility parameter, diffusivity, viscosity, mechanical, and thermophysical properties of pristine asphalt and graphene-modified binders. This study provides a molecular framework for optimizing the thermodynamic compatibility between asphalt components and graphene nanofiller and enhancing thermomechanical properties by tailoring filler percentages. The uniaxial deformation simulations performed at different strain rates demonstrate that the yield stress and postyield softening can be improved just by adding 2 wt. % of graphene filler. The increased toughness in graphene-modified binders strongly correlates with the predicted higher noncovalent intermolecular forces, lower diffusivity of asphalt components, and increased zero-shear equilibrium viscosity compared to the pristine asphalt. The glass transition temperature of asphalt is enhanced by about 26 K for the 2 wt. % graphene-reinforced asphalt composite. Density functional theory (DFT), natural energy decomposition analysis (NEDA), noncovalent interaction (NCI) analysis, and steered molecular dynamics (SMD) simulations were employed to probe the molecular mechanisms governing graphene-asphalt interactions. The multiscale simulations reveal that the strong interfacial interactions between graphene and polar asphalt components, dominated by π-π stacking and dispersion forces, are responsible for the mechanical reinforcement of the asphalt matrix. The resemblance of predicted data with experimental results in many cases further substantiates the applicability of a theoretical framework for the rational design of graphene-modified asphalt binders with desired physicochemical properties.

To assess the efficacy of a mixed-dimensional van der Waals (vdW) heterostructure in modulating the optoelectronic responses of nanodevices, the charge transport properties of the transition-metal dichalcogenide (TMD)-based heterostructure comprising zero-dimensional (0D) WS2 quantum dots (QDs) and two-dimensional (2D) MoS2 flakes are critically analyzed. Herein, a facile strategy was materialized in developing an atomically thin phototransistor assembled from mechanically exfoliated MoS2 and WS2 QDs synthesized using a one-pot hydrothermal route. The amalgamated photodetectors exhibited a high responsivity of ∼8000 A/W at an incident power of 0.05 nW of white light, surpassing that of the pristine MoS2 devices. Furthermore, the detectivity of pristine MoS2, which was on the order of 1010, increased to 1012 Jones for the WS2 QDs/MoS2 heterostructure photodetector, outperforming other WS2-based materials. The quasiparticle band gap and density of states (DOS) are further analyzed to elucidate the photophysics of the WS2 QD/MoS2 hybrid assembly. The difference in the work function between MoS2 and WS2 QDs gives rise to an electric field across the 0D-2D interface, facilitating effective charge separation and migration and contributing to the enhancement of photoresponsivity. The analysis of optical responses using density functional theory (DFT) revealed stronger absorption and less reflection over a broader spectrum of wavelengths for the heterostructure compared to the pristine materials. The estimated optical conductivity aligns well with the experimentally predicted maximum photoresponsivity under visible light, which is attributed to the high absorbance of 2D MoS2. Combining diverse spectroscopic and imaging techniques with quantum simulation provides insights that clarify the pertinence of 0D-2D TMDs in designing phototransistors.

The electronic structure and properties of 2D-2D interfaces formed by monolayer (1L) and bilayer (2L) graphene (G) and tungsten diselenide (WSe2) materials are probed within the framework of state-of-the-art density functional theory (DFT)-based methods. The electronic structure theory calculations untangle the intricate photophysics of G-supported WSe2 heterostructures influenced by crucial factors, such as intra- and interlayer coupling, symmetry breaking, and spin-orbit coupling (SOC). The charge transport from G to WSe2 layers creates an interface dipole, and the interlayer coupling breaks the centrosymmetric environment of the pristine 2L materials, which may contribute to enhancing linear and nonlinear optical responses. The extent of sublattice symmetry breaking is more pronounced for heterostructures comprising 2L G with AB (Bernal) stacking, leading to the band gap opening of the G layer on the order of 15-24 meV. As revealed by the calculated optical functions employing DFT combined with the Kubo-Greenwood formalism, attaching 2L WSe2 to 2L G results in stronger absorption over a wider spectrum of wavelengths. The second-harmonic generation (SHG) signal is intensified for the 2L G-supported WSe2 heterostructures and impacted by the extent of inversion symmetry breaking, the SOC effect, and the stacking order of G layers. The G-WSe2 heterostructures are predicted to enable more effective charge separation from excitons compared to pristine materials. The estimation of photoresponsivity and external quantum efficiency for a heterojunction G-WSe(2)p-n diode further confirms the efficacy of the G-WSe2 heterostructure in photodetectors, especially for the detection of high-energy photons in the ultraviolet spectrum. The acquired information is highly beneficial in designing functional 2D-2D heterostructures as an alternative to traditional metal-semiconductor interfaces for its application in electronic devices such as field-effect transistors.

The effects of graphene (G) nanofiller content on enhancing the mechanical and thermal resistance of the polyvinyl alcohol (PVA) matrix are disentangled by performing all-atom classical molecular dynamics (MD) simulations. The crux of the computational work is to assess several key performance-limiting factors of the functional hybrid material, including the strain rate, temperature, and the size and distribution of the graphene nanofiller. Adding graphene nanofiller to the polymer results in more compact polymer chains, with the most significant impact observed in the 2% graphene composite. Uniaxial compression MD simulations revealed that the yield strength of the material is impacted by the proportion of nanofiller present. Specifically, the calculated stress-strain responses at a strain rate of 1.5 × 108 s-1 show that incorporating 2% graphene nanofiller remarkably enhances the yield strength. Conversely, increasing the graphene content to 5-10% led to a reduction in yield stress, which is primarily attributed to the disruption of hydrogen bond networks and destabilization of non-covalent interactions. Further analysis shows that increasing the strain rate led to higher yield stress in the G-PVA composite, while elevated temperatures caused its yield stress to decrease. Additionally, the glass transition temperature of the PVA composite rises with the graphene content and strongly correlates with the polymer chain mobility. The proposed theoretical approach may serve as a quantitative framework for elucidating the crucial role of interfacial interaction between polymers and nanomaterials in modulating the conformational, thermodynamic, and macroscopic properties of the hybrid materials.

The modulation of bulk properties including the cohesive strength and the solubility of the asphaltenes, due to the inclusion of graphene nanosheets and the thermoplastic polymer, is probed by performing all-atom classical molecular dynamics (MD) simulations. The impact of morphological heterogeneity, including the size of the aromatic core of the asphaltene molecule, the nature of the heteroatom attached to the aromatic core, the orientation of the graphene nanosheets, and the surface area of the nanomaterial, on the bulk properties of the model systems of nanocomposites and interfaces is explored. The cohesive strength of the asphaltene composites is significantly enhanced by the introduction of graphene nanosheets. The addition of styrene–butadiene–styrene (SBS) block copolymer into the graphene-reinforced asphaltene systems improves the cohesive strength, structural plasticity, and compatibility between the nanomaterial and the asphaltenes. The π–π stacking interaction between the graphitic surface and the aromatic core of the asphaltene is identified to be the major driving force for modulating the cohesive strength. The dispersion interaction maximizes in the hierarchical layered structure compared to the randomly oriented structure of the graphene nanosheets and the asphaltene molecules. The energetics of non-covalent interaction are further assessed within the framework of dispersion-corrected density functional theory (DFT)-based methods. The DFT-derived adsorption energies and thermochemical properties substantiate the stronger interaction and the thermodynamic favorability of the adsorption processes in both the gas phase and solvent medium (toluene). The simulated IR and Raman spectra are also analyzed to reveal the nature of the interaction.

The subtle interplay of non-covalent interaction in enhancing the compatibility between the graphene-based material and the oligomers of polyvinyl alcohol (PVA) and polyacrylamide (PAM) in the solvent phase is unraveled within the framework of all-atom classical force field-based molecular dynamics (MD) simulations. The decomposition of binding free energy analysis demonstrates that the interaction between polymer segments and graphene (G)-surface crucially emanates from the van der Waals (vdW) interactions, while the adsorption of polymer chains on the graphene oxide (GO)-surface is influenced by vdW and electrostatic interactions. The influence of diverse factors including the strain rate, the size of the nanofiller, the number of oligomers, and the thermal quenching rate on controlling the morphology, mechanical, and thermophysical properties of the graphene-reinforced polymer nanocomposites are further explored. The uniaxial deformation simulations of the graphene-reinforced PVA and PAM matrices show that the interfacial mechanical strength is escalated for the G-PVA nanocomposite. The inclusion of graphene nanofiller reduces the polymer chain mobility and increases the intermolecular interaction, which in turn enhances the toughness of the graphene-polymer composites. Increasing the strain rate raises the yield strength and modulus, making the composites appear stronger and stiffer. As evidenced by the predicted glass transition temperature, the thermal stability of the PVA and PAM matrices is significantly improved by the graphene reinforcement.

To combat mischievous coronavirus disease followed by continuous upgrading of therapeutic strategy against the antibody-resistant variants, the molecular mechanistic understanding of protein-drug interactions is a prerequisite in the context of target-specific rational drug development. Herein, we attempt to decipher the structural basis for the inhibition of SARS-CoV-2 main protease (Mpro) through the elemental analysis of potential energy landscape and the associated thermodynamic and kinetic properties of the enzyme-inhibitor complexes using automated molecular docking calculations in conjunction with classical force field-based molecular dynamics (MD) simulations. The crux of the scalable all-atom MD simulations consummated in explicit solvent media is to capture the structural plasticity of the viral enzyme due to the binding of remdesivir analogues and ascertain the subtle interplay of noncovalent interactions in stabilizing specific conformational states of the receptor that controls the biomolecular processes related to the ligand binding and dissociation kinetics. To unravel the critical role of modulation of the ligand scaffold, we place further emphasis on the estimation of binding free energy as well as the energy decomposition analysis by employing the generalized Born and Poisson-Boltzmann models. The estimated binding affinities are found to vary between -25.5 and -61.2 kcal/mol. Furthermore, the augmentation of inhibitory efficacy of the remdesivir analogue crucially stems from the van der Waals interactions with the active site residues of the protease. The polar solvation energy contributes unfavorably to the binding free energy and annihilates the contribution of electrostatic interactions as derived from the molecular mechanical energies.

The key concept of Slater-type orbitals (STOs) underpinning quantum chemical calculations of polyatomic systems has been elucidated via a discourse on mathematical challenges of solving immanent multicenter integrals in density functional theory (DFT). Two types of orbitals viz. Gaussian-type orbitals (GTOs) and STOs are being discussed about their importance in atomic orbital-based calculations and compared their advantages and disadvantages in solving chemistry-related problems of molecules. The third type of orbitals obtained through plane-wave basis sets are excluded in this discussion, as they are mostly used to solve condensed-phase problems. The rudiments of STOs have been discussed without radical analysis of programmatic implementations of mathematical algorithms. The discussions are mainly focused on the DFT calculations, and the concepts of various Slater atomic basis sets are being introduced. In the final part of the article, a few specific examples are considered related to the application of DFT-STOs to different chemical problems. We place emphasis on benchmark studies of simple molecular structures, excitation energy calculations, excitation energy spectrum of UO22+ as well as resonance Raman spectrum analysis.

Quantum chemical computations using both density functional theory and coupled-cluster theory methods, in conjunction with a polarizable continuum model for treatment of structures in solution, were carried out on a series of small water anions [(H2O)n]•־, n = 2, 3, 4, 5, and 16. Location of the excess electron was probed from a partition of electron densities using ELF and AIM techniques. For each size n of the [(H2O)n]•־ system, two distinct structural motifs are identified: a classical water radical anion formed by hydrogen bonds and a hydrated electron in which the excess electron is directly interacting with H atoms. Both motifs have comparable energy content and likely coexist in aqueous solution.

The adequacy of the inclusion of spacer units in the metal-free D−π–A organic dyes concerning the augmentation of dye-sensitized solar cell (DSSC) efficiency has been examined through the excited-state simulations of the charge injection and recombination processes at the dye–semiconductor interface. Within the framework of the time-dependent density functional theory, the proposed computational studies focus on the precise evaluation of pivotal factors controlling the rates of photoinduced charge-transfer and energy-transfer processes, including electronic coupling, reorganization energy, and threshold energy barrier in the semiclassical Marcus formalism. The estimation of the fluorescent state appears to be the crucial step while explaining the ultrafast electron injection process and the charge recombination at the Marcus inverted region, as revealed by the obtained results. The retardation of charge recombination is facilitated by the insertion of a thiophene moiety between the π-bridge and the acceptor units. The estimated cold electron injection efficiencies deploying the Onsager–Braun theory, which rely on the computations of cold electron injection lifetime and cold electron lifetime, show a linear correlation with the experimental photovoltaic parameters of the DSSC comprising short-circuit current density, open-circuit voltage, and power conversion efficiency. The outcomes of the present investigation establish a basis for unraveling the mechanism of intricate dynamical processes upon photoexcitation of the sensitizers, as well as devising plausible routes for functional DSSC materials.

Negative thermal quenching (NTQ), an abnormal phenomenon that the intensity of photoluminescence (PL) increases with increasing temperature, has essentially been restricted to either bulk semiconductors or very low temperatures. Here, we report a delayed fluorescence copper-organic framework exhibiting negative thermal quenching (NTQ) of photoluminescence, which is driven by the fluctuation between the localized and delocalized form of its imidazole ligand. The process is completely reversible on cooling/heating cycles. This study opens a new avenue to explore the electronically switchable NTQ effect in coordination networks and further to develop the NTQ-based light-emitting diodes.

The present review article focuses on the impact of the Jahn-Teller effect (JTE) including hidden JTE and pseudo JTE on the ground and low-lying electronic structures of small transition, main group, and mixed metal clusters. The discussions are based on the results acquired from the quantum chemical analysis involving complete active space multiconfiguration self-consistent field (CASMCSCF or CASSCF) together with multireference singles and doubles configuration interaction (MRSDCI) theories. Related computational results from density functional (DFT) and coupled cluster (CC) theories, and the available experimental evidences on the JT-distorted structures are also included for comparative analysis. The role of the relativistic effects on several heavy metal clusters is discussed in detail, since these effects could lead to either enhancement or the quenching of the JTE. The final section of the review manifests the JT-distortion of several mixed metal clusters of icosahedral symmetry and they are explained through a much simpler shell structure (jellium) model.

Applicability of Hammett parameters (σ m and σ p ) was tested in extended π-systems in gas phase. Three different model graphene systems, viz. 5,5-graphene (GR), 3-B-5,5-graphene (3BGR), and 3-N-5,5-graphene (3NGR), were designed as extended π-systems, and interactions of various nitrobenzene derivatives (mainly m- and p-substituted together with some multiple substitutions) on such platforms were monitored using density functional theory (M06/cc-pVDZ, M06/cc-pVTZ, M06/sp-aug-cc-pVTZ) and Møller-Plesset second-order perturbation (MP2/cc-pV-DZ) theory. Offset face to face (OSFF) stackings were found to be the favored orientations, and reasonable correlations were found between binding energies (ΔEB) and the ∑|σ m | values of the substituted nitrobenzenes. It was proposed previously that |σ m | contains information about the substituents' polarizability and controls electrostatic and dispersion interactions. The combination of ∑|σ m | and molar refractivity (as ∑Mr) or change in polarizability (Δα: with respect to benzene) of nitrobenzene derivatives generated statistically significant correlation with respect to ΔEB, thereby supporting the hypothesis related to the validity of |σ m | correlations. The |σ p | parameters also maintain similar correlations for the various p-substituted nitrobenzene derivatives together with several multiply-substituted nitrobenzene derivatives. The correlation properties in such cases are similar to the |σ m | cases, and the energy partition analysis for both the situations reveled importance of electrostatic and dispersion contributions in such interactions. The applicability of Hammett parameters was observed previously on the restricted parallel face to face orientation of benzene···substituted benzene systems, and the present results show that such an idea could be used to predict ΔEB values in OSFF orientations, if the scaffolds are designed in such a way that substituted benzene systems cannot escape their π-clouds.

Functionalized graphene – metal nano-conjugates are used as Raman probes, in recent years, for trace level identification of materials having specific Raman active modes. In the present paper, model Raman probes were modeled through conjugation of Au4 and Ag4 clusters with functionalized graphene systems. In silico models of functionalized (5,5)-graphene sheets were designed at the density functional theory (DFT) level through attachments of epoxy, -OH and –NH(CH3)2SH/-CONH(CH3)2SH groups. Model Raman probes were designed through attachment of Au4 and Ag4 clusters to the functional sites. Full geometry optimizations followed by vibrational analysis were carried out to ensure that the designed Raman probes have acceptable geometric characteristics to attach Raman-active molecules to the metal site. Pyridine was used as a test system to investigate the functionality of such model Raman probes through attachment with the metal clusters. It was observed that the chemical effects due to such attachments increase the Raman intensities (RI) of specific Raman modes of pyridine (in-plane symmetric bending (1040 cm-1) and asymmetric stretch-bend (1634 cm-1)), which are too weak in the isolated molecule. Furthermore, the suggested in silico system could provide an important model for basic understanding of RI-enhancements of molecules through increase of the size of the metal clusters, as the observed enhancement was found to be dependent on the polarizability of the metal clusters attached to the molecule of interest.

Geometries and electronic properties related to the ground state stabilities of several Si12M2 clusters (M: second-row (Nb and Mo) and third-row (Ta and W) transition metals, and their mixed bimetallic clusters M2: NbMo and TaW) were explored using density functional theory (DFT) computations. The computed results show that two different structural motifs emerge as the global energy minima of such clusters. They are basically singlet tubular structures in either a C2v prism (1A1) or a C6v antiprism (1A1) form. Other structural shapes are also possible for higher-energy isomers and in higher spin states. 58-valence electron systems including Nb2Si12, Ta2Si12, Mo2Si122+, W2Si122+, NbMoSi12+ and TaWSi12+ are thermodynamically stable as C2v prism global minima on the corresponding potential energy surfaces. Clusters containing 60 valence electrons include Mo2Si12, W2Si12, Nb2Si122-, Ta2Si122-, NbMoSi12- and TaWSi12- and they prefer a C6v anti-prism form. In the mixed MoNbSi12 and TaWSi12 open-shell systems, both resulting C2 (2A) and C2v (2A1) forms are nearly degenerate. The formation of Si12M2 clusters in such specific ground state symmetry is explained using the Jellium model and orbital interaction analyses. The investigations lead further to a proposal for a simple model of a bimetallic configuration using the nature of interactions of the transition metal d-d dimeric bond with the Si12 host, to interpret the formation of such M2Si12 clusters.

A comprehensive review on geometric and electronic structures, spectroscopic and energetic properties of small niobium clusters in the range from two to twenty atoms, Nb-n, n = 2-20, in three different charged states is presented including a systematic comparison of quantum chemical results with available experimental data to assign the lowest-lying structures of Nbn clusters and their IR spectra and some basic thermochemical parameters including total atomization (TAE) and dissociation (De)energies based on DFT and CCSD(T) results. Basic energetic properties including electron affinities, ionization energies, binding energies per atom, and stepwise dissociation energies are further discussed. Energetic parameters of small sizes often exhibit odd-even oscillations. Of the clusters considered, Nb-2, Nb-4, Nb-8 and Nb-10 were found to be magic as they hold the numbers of valence electrons corresponding to the closed-shell in the electron shells [1S/1P/2S/1D/1F ...]. Nb-10 has a spherically aromatic character, high chemical hrT high chemical hardness and large HOMO-LUMO gap. The open-shell Nb-15 system is also particularly stable and can form a highly symmetric structure in all charged states. For species with an encapsulated Nb atom, an electron density flow is present from the cage skeleton to the central atom, and the greater the charge involved the more stabilized the cluster is.

Low-frequency vibrations coupled to high-frequency modes are known to influence the hydrogen bond strengths in a weakly interacting dimer. In this context, various acetic acid and acetamide dimers were analyzed using Møller-Plesset second-order perturbation (MP2) and density functional theory (DFT)-based approaches with explicit anharmonicity corrections. The computed low-frequency fundamentals as well as the high-frequency modes, which were found to be related to hydrogen bonding (OH/NH stretching modes), were analyzed and their computed intensities were correlated with their hydrogen-bond strengths/binding energies. There are similarities in the nature of eight low-frequency fundamentals of these two dimers, and the in-plane bending and stretch-bend fundamentals of the different dimers of these two species (in this low-frequency region) have specific roles in their relative stability order. The computed linear correlations were further verified against the results from coupled cluster calculations including triple excitation (CCSD(T)), Gaussian-G4 (G4), Gaussian-G2-MP2 (G2MP2) and complete basis set (CBS-QB3) methods of high accuracy energy calculations. As a consequence of such linear correlations, an additive property of local fragment energies (responsible for hydrogen bonding) was found to be a valid approximation to predict the binding energies of such dimers and the idea was found to be extendable to the other homologues of these acids/amides.

In previous papers (Nguyen et al. J. Phys. Chem. C2008, 112, 5662-5667 and J. Phys. Chem. C2009, 113, 18914-18926), formation of H-2 molecules from ammonia alane monomer (AAl) and dimers (AAl)(2) was shown to be facilitated by the addition of one or more alane or ammonia molecules that can play the role of efficient bifunctional catalyst. Ammonia alane emerges as a good starting compound for building up materials for chemical hydrogen storage (CHS). Further exploration of the products based on the H-2 release from ammonia alane were carried out using coupled-cluster theory computations together with the aug-cc-pVTZ basis set (based on MP2/aug-cc-pVDZ optimized geometries). Our ab initio MO calculations for the first time led to the identification of cyclotrialazane [(H2AlNH2)(3)], alazine [(HAlNH)(3)], and its oligomer [H2Al(HNAlH)(2)NH2] that are produced along the multistep dehydrogenation processes from the reactions of ammonia alane and AlH3NH2AlH2NH3. The formation of alazine (homologue of borazine) as the final product in our H-2 elimination reactions is an important feature because of its long-debated existence. The present reaction path analyses show that the formation of this compound is an important phenomenon for explaining the entire dehydrogenation process.