Hot carrier creation in a nanoparticle dimer-molecule composite.

Light-matter interactions have garnered considerable interest owing to their burgeoning applications in quantum optics and plasmonics. Utilizing first principles calculations, this work explores the hot carrier (HC) generation and distribution within a composite system made up of a plasmonic nanoparticle dimer and linear polycyclic aromatic hydrocarbon (PAH) molecules. We examine the spatial and energetic distributions of HCs by initiating photoexcitation and allowing localized surface plasmon dephasing. By positioning PAH molecules within the plasmonic nanodimer's gap region, our investigation uncovers HC tuning. Notably, depending on the size of the PAH molecules, there are significant alterations in the HC distribution. Hot electrons (HEs) are distributed across both the nanodimer and the PAH molecule, while hot holes (HHs) become entirely localized on the PAH as the PAH grows larger. These findings improve our understanding of plasmon-molecule coupled states and provide guidance on how to customize HC distributions through the creation of hybrid plasmonic materials.

The impact of a dopant atom on the distribution of hot electrons and holes in Au-doped Ag nano-clusters.

The generation of hot carriers (HCs) through the excitation of localized surface plasmon resonance (LSPR) in metal nanostructures is a fascinating phenomenon that fuels both fundamental and applied research. In this study, we employ first principles real-time time-dependent density-functional theory (rt-TDDFT) calculations to elucidate the creation and distribution of HCs within Au-doped Ag nanoclusters: Ag11Cl3P7H21, Ag10AucoreCl3P7H21, and Ag10AusurfCl3P7H21 nanoclusters. Our findings indicate that adjustments in HC distribution are achievable through the Au dopant atom, and precise control of HC distribution is possible by manipulating the location of the Au dopant atom. When employing a Gaussian laser pulse tailored to match the LSPR frequency, a substantial accumulation of HCs in the Ag-P bond is observed. This finding suggests a weakening of the Ag-P bonds and, consequently, the initiation of bond stretching. We propose that these findings open up possibilities for tuning HCs in Au-doped chemically functionalized Ag nanoclusters.

Plasmon-induced hot carrier distribution in a composite nanosystem: role of the adsorption site.

The generation of hot carriers (HCs) through the excitation of localized surface plasmon resonance (LSPR) in metal nanostructures is a fascinating phenomenon that fuels both fundamental and applied research. However, gaining insights into HCs at a microscopic level has posed a complex challenge, limiting our ability to create efficient nanoantennas that utilize these energized carriers. In this investigation, we employ real-time time-dependent density functional theory (rt-TDDFT) calculations to examine the creation and distribution of HCs within a model composite system consisting of a silver (Ag) nanodisk and a carbon monoxide (CO) molecule. We find that the creation and distribution of HCs are notably affected by the CO adsorption site. Particularly, when the CO molecule adsorbs onto the hollow site of the Ag nanodisk, it exhibits the highest potential among various composite systems in terms of structural stability, enhanced orbital hybridization, and HC generation and transfer. Utilizing a Gaussian laser pulse adjusted to match the LSPR frequency, we observe a marked buildup of hot electrons and hot holes on the C and O atoms. Conversely, the region encompassing the C-O bond exhibits a depletion of hot electrons and hot holes. We believe that these findings could have significant implications in the field of HC photocatalysis.

Exploring intermixed magnetic nanoparticles: insights from atomistic spin dynamics simulations.

Binary nanoparticles, composed of both rare-earth elements with substantial magnetic properties and transition metals known for their high magnetic ordering temperatures, hold great promise as innovative materials for novel magnetic applications. In this study, we employ an atomistic spin dynamics framework to investigate how the magnetic properties change at finite temperatures in mixed NiGd nanoparticles. We specifically examine parameters such as saturation magnetization and spin-reorientation in relation to the nanoparticle's size, which ranges from 4 nm to 16 nm, and composition. Our findings reveal that Ni75Gd25 nanoparticles demonstrate exceptional magnetic properties at finite temperatures, marked by significantly increased saturation magnetizations and magnetic ordering temperatures. In contrast, nanoparticles containing 50% and 75% Gd contents exhibit notably reduced saturation magnetizations and magnetic ordering temperatures. Theoretical findings of our study shed light on the pivotal role that the Gd content plays in determining the magnetic behaviour at finite temperatures.

Plasmon induced hot carrier distribution in Ag20 -CO composite.

The interaction between plasmons and the molecules leads to the transfer of plasmon-induced hot carriers, presenting innovative opportunities for controlling chemical reactions on sub-femtosecond timescales. Through real-time time-dependent density functional theory simulations, we have investigated the enhancement of the electric field due to plasmon excitation and the subsequent generation and transfer of plasmon-induced hot carriers in a linear atomic chain of Ag20 and an Ag20 -CO composite system. By applying a Gaussian laser pulse tuned to align with the plasmon frequency, we observe a plasmon-induced transfer of hot electrons from the occupied states of Ag to the unoccupied molecular orbitals of CO. Remarkably, there is a pronounced accumulation of hot electrons and hot holes on the C and O atoms. This phenomenon arises from the electron migration from the inter-nuclear regions of the C-O bond towards the individual C and O atoms. The insights garnered from our study hold the potential to drive advancements in the development of more efficient systems for catalytic processes empowered by plasmonic interactions.

Plasmon induced hot carrier generation in a pyridine@Au20 composite.

Using time-dependent density functional theory calculations, we have investigated the generation of hot carriers (HCs) in a system comprising a pyridine molecule and a tetrahedral Au20 plasmonic cluster. Our findings indicate that the decay of the localized surface plasmon resonance (LSPR) induced in the pyridine@Au20 system by a laser pulse facilitates the direct transfer of hot electrons from the occupied states of the Au20 cluster to the unoccupied molecular orbitals of pyridine. Notably, we have identified that the interparticle gap distance between the Au20 cluster and the pyridine molecule plays a critical role in controlling the generation of HCs. By precisely controlling the interaction between the plasmonic cluster and the molecule, we can effectively manipulate the energy distribution of the generated HCs. These insights have the potential to drive advancements in the development of more efficient systems for plasmonic catalysis.

Interface plasmon damping in the Cd33Se33/Ti2C MXene heterostructure.

MXenes, a class of two-dimensional materials, have shown immense potential in various applications such as energy storage, electromagnetic shielding, solar cells, smart fabrics, optoelectronics, and plasmonics. In this study, we employ first-principles density functional theory (DFT) and time-dependent DFT calculations to investigate a semiconductor-metal heterostructure composed of a Cd33Se33 cluster and Ti2C MXene monolayer flakes. Our research focuses on the formation and damping of localized surface plasmon resonances (LSPRs) within this heterostructure. We discover that the Cd33Se33/Ti2C interface gives rise to a Schottky barrier. Importantly, this interface formation results in the damping of the Ti2C LSPR, thereby facilitating the transfer of electrons into the Cd33Se33 cluster. By directly visualizing the LSPR damping phenomenon, our study enhances our understanding of the semiconductor-MXene interface and provides novel insights for the design of MXene-based photocatalysts.

Optical properties of in-plane chemically ordered i-MAX structures.

The prospects of novel materials with intriguing features increases with greater chemical diversity and structural complexity. In this work, we have investigated the electronic and optical characteristics of the atomically laminated i-MAX structures [(Mo2/3Sc1/3)2 AC with A = Al, Ga, In, Sn] using first-principles density functional theory calculations. We demonstrate how the electronic states at the Fermi level are affected by changes in the A element, and how this has a significant impact on the electronic and optical characteristics of the i-MAX structures. Additionally, the investigated systems exhibit optical reflectivity of more than 80% in the low energy region of the electromagnetic spectrum, making them suitable for coatings that lower solar heating. The results of this theoretical investigation help us to better comprehend the i-MAX's optical characteristics.

Unravelling the impact of oily alkane molecules on the optical properties of the calcite(10.4) surface.

For a variety of commercial and environmental applications, including oil production, CO2 storage, and contaminant treatment, the endurance of organic molecules on calcite surfaces is of interest. In this study, we have examined the effects of adsorption of dodecane molecules on the structural, energetic, electronic, and optical properties of the calcite(10.4) surface using density functional theory (DFT) and time-dependent DFT. We demonstrate that dodecane molecules prefer to align themselves parallel to the calcite(10.4) surface and that the nature of their interaction is predominantly ionic. We also notice intriguing modifications in the photoabsorption spectra. The findings of this study suggest that the characteristics of calcite can be influenced by organic molecules that have been adsorbed from the environment.

Photo-response of water intercalated Ti3C2O2 MXene.

Two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides (MXenes) have drawn a lot of attention because of their unique physicochemical properties. Recent experimental and theoretical findings reveal that water intercalation in MXene results in surface reconstruction and hydrolysis. In the current study, we investigated the electronic and optical characteristics of the water-intercalated Ti3C2O2 MXene using first-principles quantum simulations via density functional theory (DFT) and time-dependent density functional theory (TD-DFT). We show that water intercalation impacts the electronic states close to the Fermi level, which has a considerable effect on the electronic and optical properties of Ti3C2O2 MXene. Importantly, we linked hydrolysis with the changes in the HOMO and LUMO states and with the optical properties. The findings in this study contribute to a better understanding of the photo-response of the water-intercalated MXene.

Coupled plasmons in aluminum nanoparticle superclusters.

Metallic nanoparticles can self-assemble into highly ordered superclusters for potential applications in optics and catalysis. Here, using first-principles quantum mechanical calculations, we investigate plasmon coupling in superclusters made of aluminum nanoparticles. More specifically, we study/compare the plasmon coupling in close-pack FCC (face-centered-cubic) and non-close-pack BCC (body-centered-cubic) superclusters. We demonstrate that the optical properties of these clusters can be fine-tuned with respect to the packing arrangement. As a key result of this work, plasmon coupling is found to be enhanced (diminished) in FCC (BCC) superclusters due to constructive (destructive) plasmon coupling. Our quantum calculations would help in the design of Al-based superclusters beneficial for plasmonics applications.

Localized surface plasmon resonances in a hybrid structure consisting of a mono-layered Al sheet and Ti3C2F MXene.

MXenes are a novel class of two-dimensional materials that exhibit unique light-matter interactions. In this work, using quantum-mechanical simulations based on the time dependent density functional theory, we investigate the electronic and optical properties of a hybrid structure consisting of a mono-layered aluminum (Al) sheet and Ti3C2F MXene. As a key result of this work, we reveal that the coupling of a mono-layered Al sheet on top of Ti3C2F MXene causes interlayer charge transfer accompanied by strong signatures of localized surface plasmon resonances (LSPRs) in the visible region of the electromagnetic spectrum. Our theoretical findings demonstrate a promising strategy to generate LSPRs in MXene-based heterostructures.

Impact of Adsorption of Straight Chain Alcohol Molecules on the Optical Properties of Calcite (10.4) Surface.

Calcium carbonate plays a central role in controlling the chemistry of the oceans, biomineralization and oil production, to name a few. In this work, using density functional theory with semiempirical dispersion corrections and simplified TD-DFT using Tamm-Dancoff approximation, we investigated the impact of the adsorption of straight chain alcohol (ethanol and pentanol) molecules on the optical properties of a calcite (10.4) surface. Our results show that ethanol and/or pentanol molecules form a well-ordered monolayer (through their hydroxyl group with carbon chains sticking away in a standing-up position) on the calcite (10.4) surface. Additionally, we found intriguing modulations in the photoabsorption spectra and circular dichroism spectra. In particular, the latter was a unique optical fingerprint for a molecule-adsorbed calcite (10.4) surface. Our findings provide useful insights into the structural and optical features of calcite-based systems at the atomic level.

Impact of packing arrangement on the optical properties of C60 cluster aggregates.

The packing arrangement of organic π-conjugated molecules in a nanoscale material can have a strong impact on their optical properties. Here, using real-time-propagation time dependent density functional theory (rt-TDDFT) calculations with the support of transition contribution maps, we study how modifications in the packing arrangement (cubic-like and chain-like aggregates composed of eight C60 molecules) and packing density (assembled at close distances with center-to-center inter-fullerene distances (d) varying from 9 Å to 11 Å) of C60 molecules affect the optical properties of cluster aggregates. The important conclusions drawn from this work are summarized as follows. For d = 9 Å, the charge transfer excitons produced by cubic and chain-like C60 cluster aggregates have highly different optical characteristics, as evidenced by the transition contribution maps. On the other hand, for d = 10 Å and 11 Å, both kinds of aggregates produce qualitatively similar optical features with the emergence of Wannier-like delocalized excitons having distinct degrees of localization and spatial distribution. The theoretical findings in this study elucidate the optical excitations in C60 cluster aggregates and could help in the design of more efficient organic devices.

Probing the self-diffusion process in Aluminium.

An in-depth understanding of the diffusion process in liquid metals is a key to design and engineering new high-performance materials. In this study, using molecular dynamics simulations supplemented with the embedded atom potential, we investigate/compare the self-diffusion process in liquid Aluminium. To understand the self-diffusion process, we analyse the radial distribution functions, velocity distributions, mean square displacements, and self-diffusion coefficients at various temperatures well above the melting temperature of Aluminium in the temperature range of 1000 K to 1800 K. As a key result, in both the [Formula: see text] and [Formula: see text] phases, the self-diffusion coefficients show a non-linear variation with rise in temperatures in the range of 1000 K to 1200 K. From 1300 K to 1800 K, the self-diffusion coefficients increase more or less monotonically with rise in temperature. We found that a higher temperature in the range of 1300 K to 1800 K leads to a greater self-diffusion coefficient, suggesting the more violent movement of the atoms around their equilibrium positions. The results presented in this work can help to understand the differences in the self-diffusion process in the technologically relevant Al phases.

Localized surface plasmon resonances and electric field confinement in titanium carbide (Ti3C2) MXene nanoclusters.

Two-dimensional metal carbides and nitrides, known as MXenes, are an emerging class of materials that are promising for a variety of applications. In this work, using time-dependent density functional theory calculations, we investigate the localized surface plasmon resonances and electric field confinement of pristine and surface-terminated [fluorinated (F) and/or oxidized (O)] mono-layered titanium carbide (Ti3C2) MXene nanoclusters. We found that the nanoclusters (Ti48C32, Ti48C32F32, and Ti48C32O32) exhibit broadband photoabsorption spectra and localized surface plasmon resonances even at low energy in the infrared region (a spectral range of interest for molecular sensing). In addition, the nanoclusters produce a sizable electric field confinement on the surface with a strength that varies with the F/O surface termination. Our findings provide significant theoretical insight into the optical and plasmonic properties of MXene nanoclusters.

Delocalized exciton formation in C60 linear molecular aggregates.

Organic semiconducting materials containing C60 molecules are efficient acceptors for planar perovskite solar cells. In this work, we theoretically investigate the optical and excitonic properties of C60 linear molecular aggregates (composed of 1 to 7 C60 molecules) via the real-time-propagation rt-TDDFT technique. In the case of a single C60 molecule, the photoabsorption peaks are dominated by localized molecular excitons. We furthermore demonstrate that, in the case of linear molecular aggregates, the photoabsorption peaks are contributed by localized molecular excitons, charge transfer excitons, and Wannier-like delocalized excitons. This result is different to the accepted theory that only localized molecular excitons or charge transfer excitons can be produced in organic semiconducting materials. This work provides additional insights into the exciton formation in C60 molecular aggregates and may help in the rational design of efficient solar cells.

Temperature-dependent electronic structure of bixbyite α-Mn2O3 and the importance of a subtle structural change on oxygen electrocatalysis.

Bixbyite α -Mn2O3 is an inexpensive Earth-abundant mineral that can be used to drive both oxygen evolution (OER) and oxygen reduction reactions (ORR) in alkaline conditions. It possesses a subtle orthorhombic → cubic phase change near room temperature that suppresses Jahn-Teller distortions and presents a unique opportunity to study how atomic structure affects the electronic structure and catalytic activity at a temperature range that is easily accessible in OER/ORR experiments. Previously, we observed that heat-treated α -Mn2O3 had a better performance as a bifunctional catalyst in the oxygen evolution (OER) and oxygen reduction reactions (ORR) (Dalton Trans. 2016, 45, 18,494-18,501). We hypothesized that heat-treatment pinned the material into a more electrochemically active cubic phase. In this manuscript, we use high-resolution X-ray diffraction to collect the temperature-dependent structures of α -Mn2O3, and then input them into ab initio calculations. The electronic structure calculations indicate that the orthorhombic → cubic phase transition causes the Mn 3d and O 2p bands to overlap and mix covalently, transforming α -Mn2O3 from a semiconductor to a semimetal. This subtle change in structure also modifies Mn-O-Mn bond distances, which may improve the activity of the material in oxygen electrochemistry. OER and ORR experiments were performed using the same electrode at various temperatures. They show a jump in the exchange current density near the phase change temperature, demonstrating the higher activity of the cubic phase.

Free Energy Surfaces and Barriers for Vacancy Diffusion on Al(100), Al(110), Al(111) Reconstructed Surfaces.

Metadynamics is a popular enhanced sampling method based on the recurrent application of a history-dependent adaptive bias potential that is a function of a selected number of appropriately chosen collective variables. In this work, using metadynamics simulations, we performed a computational study for the diffusion of vacancies on three different Al surfaces [reconstructed Al(100), Al(110), and Al(111) surfaces]. We explored the free energy landscape of diffusion and estimated the barriers associated with this process on each surface. It is found that the surfaces are unique regarding vacancy diffusion. More specically, the reconstructed Al(110) surface presents four metastable states on the free energy surface having sizable and connected passage-ways with an energy barrier of height 0.55 eV. On the other hand, the reconstructed Al(100)/Al(111) surfaces exhibit two/three metastable states, respectively, with an energy barrier of height 0.33 eV. The findings in this study can help to understand surface vacancy diffusion in technologically relevant Al surfaces.

Localized surface plasmon resonances of a metal nanoring.

Using the linear combination of atomic orbitals real-time-propagation rt-TDDFT technique (LCAO-rt-TDDFT) and transition contribution maps, we study the optical and plasmonic features of a metal nanoring (made up of sodium atoms) with respect to the modulation in the ring thickness from a sharp edge (one-atom-thick) to a flat edge (four-atoms-thick). The birth of the localized surface plasmon resonance was accessed by many factors including the number of contributing electron-hole transitions, the relative strengths of these contributions, and the nature of the induced charge density oscillation. We reveal that the occurrence of a large number of contributing electron-hole transitions to an absorption peak cannot be treated as an indicator of plasmonicity. Nonetheless, plasmonicity can be accessed from the transition contribution map (occurrence of many spots with strong contributions and distributed on a large domain of energy) and from the profile of the induced charge density. Our results are useful for designing ultra-small plasmonic devices based on metal nanorings as building blocks.