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The lithium-sulfur (Li-S) battery is one of the most promising substitutes for current energy storage systems because of its low cost, high theoretical capacity, and high energy density. However, the high solubility of intermediate products (i.e., lithium polysulfides) and the resultant shuttle effect lead to rapidly fading capacity and a low coulombic efficiency, which hinder the practical application of Li-S batteries. In this study, block copolymers are constructed with both an ethylene oxide unit and a styrene unit and then used as binders for Li-S batteries. Electrochemical performance improvements are attributed to the synergistic effects contributed by the different units of the block copolymer. The ethylene oxide unit traps polysulfide, which bonds strongly with the intermediate lithium polysulfide, and enhances the transport of lithium ions to reach high capacity. Meanwhile, the styrene unit maintains cathode integrity by improving the mechanical properties and elasticity of the constructed block copolymer to accommodate the large volume changes. By enabling multiple functions via different units in the polymer chain, high sulfur utilization is achieved, polysulfide diffusion is confined, and the shuttle effect is suppressed during the cycle life of Li-S batteries, as revealed by operando ultraviolet–visible spectroscopy and S K-edge X-ray absorption spectroscopy.

As a half-reaction of electrolytic water-splitting for hydrogen generation, the oxygen evolution reaction (OER) is the major bottleneck due to the sluggish kinetics of the four-electron transfer reaction. Developing high-efficiency and cost-effective OER electrocatalysts is crucial to the advancement of water-splitting. Besides the conventional metal-based nanoparticle catalysts, constructing single-atom catalysts (SACs) on two-dimensional (2D) materials has become an important research direction in recent years. In this review, we summarize the recent strategies for the synthesis of SACs, the experimental and theoretical studies of 2D material-based SACs to enhance the OER performance, and the rational design principles of SACs toward the OER, as well as the challenges and future directions. A discussion is provided for a better understanding of the OER, to guide the optimization of electrocatalysts, and for possible future candidates of SACs.

Enzymes feature the concerted operation of multiple components around an active site, leading to exquisite catalytic specificity. Realizing such configurations on synthetic catalyst surfaces remains elusive. Here, we report a nanoparticle/ordered-ligand interlayer that contains a multi-component catalytic pocket for high-specificity CO2 electrocatalysis. The nanoparticle/ordered-ligand interlayer comprises a metal nanoparticle surface and a detached layer of ligands in its vicinity. This interlayer possesses unique pseudocapacitive characteristics where desolvated cations are intercalated, creating an active-site configuration that enhances catalytic turnover by two orders and one order of magnitude against a pristine metal surface and nanoparticle with tethered ligands, respectively. The nanoparticle/ordered-ligand interlayer is demonstrated across several metals with up to 99% CO selectivity at marginal overpotentials and onset overpotentials of as low as 27 mV, in aqueous conditions. Furthermore, in a gas-diffusion environment with neutral media, the nanoparticle/ordered-ligand interlayer achieves nearly unit CO selectivity at high current densities (98.1% at 400 mA cm−2). The complex, multi-component environments found in enzymes induce high catalytic specificity, but are difficult to achieve in synthetic catalysts. Now, researchers report a catalyst comprising a dynamic, ordered layer of ligands above a nanoparticle surface that creates a pocket to facilitate CO2 electroreduction.

Solid-state Li–S batteries are attractive due to their high energy density and safety. However, it is unclear whether the concepts from liquid electrolytes are applicable in the solid state to improve battery performance. Here, we demonstrate that the nanoscale encapsulation concept based on Li2S@TiS2 core–shell particles, originally developed in liquid electrolytes, is effective in solid polymer electrolytes. Using in situ optical cell and sulfur K-edge X-ray absorption, we find that polysulfides form and are well-trapped inside individual particles by the nanoscale TiS2 encapsulation. This TiS2 encapsulation layer also functions to catalyze the oxidation reaction of Li2S to sulfur, even in solid-state electrolytes, proven by both experiments and density functional theory calculations. A high cell-level specific energy of 427 W·h·kg–1 is achieved by integrating the Li2S@TiS2 cathode with a poly­(ethylene oxide)-based electrolyte and a lithium metal anode. This study points to the fruitful direction of borrowing concepts from liquid electrolytes into solid-state batteries.

A crystalline solid electrolyte interphase Li2CO3 material with a large band gap shows promise toward next-generation all-solid-state lithium batteries (ASSLBs). However, the inferior ionic diffusivity restricts such structures to a real battery setup. Herein, based on density functional theory calculation and Python materials genomics, we theoretically develop the chemistry and local structural motifs to build a mixed boron-carbon framework Li2+xC1-xBxO3 (LCBO). We examine the electrochemical and chemical stabilities of LCBO-electrode interfaces by analyzing the thermodynamics of formation of interfacial phases. Interestingly, the LCBO material is automatically protected from further decomposition through the self-generated resistive interphase (Li2CO3 and Li3BO3), which gives a wide range of operating potential. LCBO shows high interfacial stability with LiCoO2, LiMnO2, and LiMn2O4. More importantly, the theoretical Li-ion migration barrier of LCBO (x = 0.375) is approximately 0.23 ± 0.02 eV through a cooperative migration mechanism. Therefore, the LCBO material combines high Li-ion diffusivity with good interfacial stability, which makes it a promising solid-state electrolyte material for ASSLBs.

Rationally designing efficient, low-cost and stable catalysts toward the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR) is of significant importance to the development of renewable energy technologies. In this work, we have systematically investigated a series of potentially efficient and stable single late transition metal atom doped phthalocyanines (TM@Pcs, TM = Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ir and Pt) as single-atom catalysts (SACs) for applications toward the OER and ORR through a computational screening approach. Our calculations indicate that TM atoms can tightly bind with Pc monolayers with high diffusion energy barriers to prevent the isolated atoms from clustering. The interaction strength between intermediates and TM@Pc governs the catalytic activities for the OER and ORR. Among all the considered TM@Pc catalysts, Ir@Pc and Rh@Pc were found to be efficient OER electrocatalysts with overpotentials ηOER of 0.41 and 0.44 V, respectively, and for the ORR, Rh@Pc exhibits the lowest overpotential ηORR of 0.44 V followed by Ir@Pc (0.55 V), suggesting that Rh@Pc is an efficient bifunctional catalyst for both the OER and ORR. Moreover, it is worth noting that the Rh@Pc catalyst can remain stable against dissolution under the pH = 0 condition. Ab initio molecular dynamic calculations suggest that Rh@Pc could remain stable at 300 K. Our findings highlight a novel family of two-dimensional (2D) materials as efficient and stable SACs and offer a new strategy for catalyst design.

Li1+xAlxTi2−x(PO4)3 (LATP) is attracting attention as a promising inorganic solid electrolyte (ISE) with potential use in all-solid-state lithium-ion batteries. The objective of this paper is to examine and understand the effect of the Al-dopant concentration on the Li-ion diffusion of LATP using density functional theory and the molecular dynamics method. By comparing Li1.16Al0.16Ti1.84(PO4)3 (LATP-0.16) and Li1.33Al0.33Ti1.67(PO4)3 (LATP-0.33) with Li1.5Al0.5Ti1.5(PO4)3 (LATP-0.50), LATP-0.50 is expected to have higher ionic conductivity. The trapping effect of Al-dopants on Li-ions is greatly reduced in LATP-0.50 due to the delocalization of polarization interactions and the depopulation of oxygen atoms, which results in a smooth energy landscape and destabilization of Li-ions. The energy difference of adjacent Li-ions and binding interaction of Li–Li due to a specific local configuration of two Li-ions alternately enable cooperative migration of Li-ions. This understanding of high Li-ion diffusion is important in interpreting the experimental results aiming to assess the effects of Al-dopants on Li-ion conductivity and can be used by researchers to engineer these materials for batteries.

Manipulating liquids with tunable shape and optical functionalities in real time is important for electroactive flow devices and optoelectronic devices, but remains a great challenge. Here, we demonstrate electrotunable liquid sulfur microdroplets in an electrochemical cell. We observe electrowetting and merging of sulfur droplets under different potentiostatic conditions, and successfully control these processes via selective design of sulfiphilic/sulfiphobic substrates. Moreover, we employ the electrowetting phenomena to create a microlens based on the liquid sulfur microdroplets and tune its characteristics in real time through changing the shape of the liquid microdroplets in a fast, repeatable, and controlled manner. These studies demonstrate a powerful in situ optical battery platform for unraveling the complex reaction mechanism of sulfur chemistries and for exploring the rich material properties of the liquid sulfur, which shed light on the applications of liquid sulfur droplets in devices such as microlenses, and potentially other electrotunable and optoelectronic devices., Manipulating liquids with tunable shape and optical functionalities in real time remains a great challenge. Here, the authors demonstrate electrotunable liquid sulfur microdroplets in an electrochemical cell and tune its characteristics in a fast, repeatable, and controlled manner.

Polymers with a broad range of properties, structural diversity, and mechanical flexibility have been adopted in all aspects of Li-S batteries. However, currently explored polymers for Li-S cathodes suffer from low conductivity, low S content, and poor cycling performance. In this first-principles study, we theoretically design a new polymer, poly(2-vinyl,1,4-phenylene sulfide), by modifying the conductive poly(1,4-phenylene sulfide) via the vinyl group to enhance its ability to vulcanize with element S. We compare the properties of the experimentally realized sulfur vulcanized polymers via condensation and our designed sulfur vulcanized polymers via crosslinking as Li-S battery cathodes, in terms of gravimetric and specific capacities, as well as structural stability during the lithiation. Overall, we find that our designed polymer possesses better conductivity, higher specific capacity and gravimetric energy density, and better kinetic stability, and restricts the shuttle effect more efficiently than the current experimentally explored one. Also, the cross-linked sulfur compounds can be activated efficiently due to the short transport lengths rather than dissolution in the electrolyte during battery operation. Therefore, we believe our designed polymer cathode is promising for practical applications. This journal is

It has been widely realized, in aqueous solution, that metal cations near a catalytic surface in the Helmholtz layer can have a significant influence on catalytic reduction processes, from CO2 reduction to H2 generation. However, the exact nature of the cation distribution, the free energy profile, and local coordination with water molecules, as well as the electrode potential dependence are still not known. For example, it is known that water molecules can form some layer structures above the surface. Are the cations in some particular positions in the water layer? What is the free energy profile of a cation as a function of its position? What is the cation density at the surface for a given bulk concentration? How do their energy profiles depend on the electrode potential? What is the trend for different cations due to their size and chemistry difference? Answering these questions is essential to understand the role of cations in aqueous based catalytic processes. In this work, using ab initio molecular dynamics (AIMD) simulations with explicit water, we provide a systematic study of the above questions for the series of alkali cations (Li+, Na+, K+, Rb+ and Cs+) on both neutral and charged Cu (111) electrodes (corresponding to electrode potentials from −2.16 V to 1.56 V vs. SHE). The results indicate that the alkali cations will remain near the electrode–electrolyte interface over a wide potential range (from −2.16 V to 1.37 V). The free energy profile obtained from thermodynamics integration shows that Na+ likes to remain near the interface, and it prefers the odd layer of the water structure. A simple model is provided to explain the underlying reason for such behavior. We also find that the surface concentration can be very high for a moderate bulk cation concentration, indicating a possible strong cation role in the catalytic process.

The hot carrier cooling occurs in most photoexcitation-induced phase transitions (PIPTs), but its role has often been neglected in many theoretical simulations as well as in proposed mechanisms. Here, by including the previously ignored hot carrier cooling in real-time time-dependent density functional theory (rt-TDDFT) simulations, we investigated the role of hot carrier cooling in PIPTs. Taking IrTe2 as an example, we reveal that the cooling of hot electrons from the higher energy levels of spatially extended states to the lower energy levels of the localized Ir-Ir dimer antibonding states strengthens remarkably the atomic driving forces and enhances atomic kinetic energy. These two factors combine to dissolute the Ir-Ir dimers on a timescale near the limit of atomic motions, thus initiating a deterministic kinetic phase transition. We further demonstrate that the subsequent cooling induces nonradiative recombination of photoexcited electrons and holes, leading to the ultrafast recovery of the Ir-Ir dimers observed experimentally. These findings provide a complete picture of the atomic dynamics in optically excited structural phase transitions., Comment: 20 pages, 8 figures

Two-dimensional (2D) Dirac cone materials exhibit linear energy dispersion at the Fermi level, where the effective masses of carriers are very close to zero and the Fermi velocity is ultrahigh, only 2-3 orders of magnitude lower than the light velocity. Such Dirac cone materials have great promise in high-performance electronic devices. Herein, we have employed the genetic algorithm methods combined with first-principles calculations to propose a new 2D anisotropic Dirac cone material, an orthorhombic boron phosphide (BP) monolayer named borophosphene. Molecular dynamics simulation and phonon dispersion have been used to evaluate the dynamic and thermal stability of borophosphene. Because of the unique arrangements of B-B and P-P dimers, the mechanical and electronic properties are highly anisotropic. Of great interest is the fact that the Dirac cone of the borophosphene is robust, independent of in-plane biaxial and uniaxial strains, and can also be observed in its one-dimensional zigzag nanoribbons and armchair nanotubes. The Fermi velocities are ∼105 m/s, on the same order of magnitude as that of graphene. By using a tight-binding model, the origin of the Dirac cone of borophosphene is analyzed. Moreover, a unique feature of self-doping can be induced by the in-plane biaxial and uniaxial strains of borophosphene and the curvature effect of nanotubes, which is greatly beneficial for realizing high-speed carriers (holes). Our results suggest that the borophosphene holds great promise for high-performance electronic devices, which could promote experimental and theoretical studies for further exploring the potential applications of other 2D Dirac cone sheets.

A sulfur-based solid-state electrolyte with the highest Li-ion conductivity shows promise toward next-generation all-solid-state lithium batteries. However, the moisture-sensitivity and (electro)ch...

LISICON-like materials are attracting attention as promising new Li-ion conductors with potential use in all-solid-state Li-ion batteries. Although the concept of cooperative diffusion mechanism has been discussed before, a detail understanding of the diffusion process is still lacking for this material. Here, an atomic-scale investigation of the Li 10 SiP 2 S 12 (LSPS)-based system using advanced simulation techniques provides valuable insights into its Li-ion conducting mechanisms. We find that Li-ion conduction in LSPS occurs through a concerted motion of interstitial and lattice Li-ions, evidenced both from molecular dynamics trajectory analysis and energy barrier calculations. The cause for the cooperative migration is the existence of a low-barrier step, by which one Li-ion's migration helps another adjacent Li-ion's migration through mutually beneficial S atoms relaxation and electrostatic interaction. Cooperative migration occurs in the channels formed by connected LiS 4 tetrahedrons through Li–Li interaction as well as dual-Li-sites. Cl-doping can enhance cooperative migration by a new low-barrier step due to more flexible PS 3 Cl and large oscillation of Li, which smoothes Li potential energy surface and enhances cooperative migration.

Oriented attachment of nanocrystals is an important route to constructing epitaxially-connected nanocrystal superlattices for various applications. During oriented attachment of semiconductor nanocrystals, neck can be formed between nanocrystals and it strongly influences the properties of the resulting superlattice. However, the neck formation mechanism is poorly understood. Here, we use in situ liquid cell transmission electron microscopy to directly observe the initiation and growth of homoepitaxial necks between PbSe nanocrystals with atomic details. We find that neck initiation occurs slowly (~ 10 s) when two nanocrystals approach to each other within an edge-to-edge distance of 0.6 nm. During neck initiation, Pb and Se atoms defuse from other facets into the gap, forming “dynamic reversible” filaments. Once the filament (neck) width is larger than a critical size of 0.9 nm, it gradually (15 s) widens into a 3-nm-wide neck. The atomic structure of the neck is further obtained using ex situ aberration-corrected scanning TEM imaging. Neck initiation and growth mechanisms are elucidated with density functional theory calculations. Our direct unveiling of the atomic pathways of neck formation during oriented attachment shed light into the fabrication of nanocrystal superlattices with improved structural order and electronic properties.

Two-dimensional (2D) materials have attracted significant interest because of their large surface-to-volume ratios and electron confinement. Compared to common 2D materials such as graphene or metal hydroxides, with their intrinsic layered atomic structures, the formation mechanisms of 2D metal oxides with a rocksalt structure are not well understood. Here, we report the formation process for 2D cobalt oxide and cobalt nickel oxide nanosheets, after analysis by in situ liquid-phase transmission electron microscopy. Our observations reveal that three-dimensional (3D) nanoparticles are initially formed from the molecular precursor solution and then transform into 2D nanosheets. Ab initio calculations show that a small nanocrystal is dominated by positive edge energy, but when it grows to a certain size, the negative surface energy becomes dominant, driving the transformation of the 3D nanocrystal into a 2D structure. Uncovering these growth pathways, including the 3D-to-2D transition, provides opportunities for future material design and synthesis in solution. Liquid phase transmission electron microscopy reveals the growth pathway of 2D cobalt oxide and cobalt nickel oxide, in which 3D nanoparticles are formed first and then spread and transform into 2D nanosheets.

Recently, many high-throughput calculation materials databases have been constructed and found wide applications. However, a database is only useful if its content is reliable and sufficiently accurate. It is thus of paramount importance to gauge the reliabilities and accuracies of these databases. Although many properties have been predicted accurately in these databases, electronic band gap is well known to be underestimated by traditional density functional theory (DFT) calculations under local density approximation (LDA), which becomes a challenging problem for materials database building. Here, we introduce MaterialGo ( http://www.pkusam.com/data-base.html ), a new database calculating the band structures of crystals using both Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional and Heyd-Scuseria-Ernzerhof (HSE) hybrid functional. Comparing different PBE databases, it is found that their band gaps are consistent when no U parameter is used for transition metal d-state or heavy element f-state to correct their self-interaction error, but rather different when PBE+ U are used, mostly because of the different values of U used in different database. HSE calculations under standard parameters will give larger band gaps that are closer to experiment. Based on the high-throughput HSE calculations over 10000 crystal structures, we might have a better understanding of the relationship between crystal structures and electronic structures, which will help us to further explore material genome science and engineering.

Summary In lithium-sulfur (Li-S) batteries, the insulating nature of sulfur and lithium sulfide (Li2S) results in large polarization and low sulfur utilization while the soluble polysulfides lead to internal shuttle upon cycling. Furthermore, the redox reaction via the dissolution-precipitation route destroys the electrode architecture by passivating the active interface responsible for the redox reaction, and thus the performance deteriorates with cycling. Here, we employ the redox chemistry of quinone to realize efficient, fast, and stable operation of Li-S batteries using Li2S microparticles. By adding a quinone derivative with tailored properties (e.g., oxidation potential, solubility, and electrochemical stability) to an electrolyte as a redox mediator (RM), initial charging of Li2S electrodes occurs below 2.5 V at 0.5C, and the subsequent discharge capacity is as high as 1,300 mAh gs−1. Moreover, deposition of dead Li2S, which was the primary cause of increasing polarization and decreasing capacity upon cycling, is effectively prevented with the RM.

The search for high efficiency and low-cost catalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is vital to overall water splitting. In this work, on the basis of first-principles calculations, we screened a series of late transition metal atoms supported on a C9N4 monolayer (TM@C9N4, where TM represents Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ir, and Pt) as electrocatalysts for both the HER and OER. Our results demonstrate that the TM atoms can be bonded with the nitrogen atoms around the hole to form stable structures, and the bonded TM atoms are stable against diffusion. Co@C9N4 exhibits high catalytic activity toward the HER. In particular, the N active sites in the Co@C9N4, Ni@C9N4, and Pt@C9N4 systems demonstrate relatively high performance for the HER. However, Co@C9N4 and Pt@C9N4 exhibit low OER activities with large overpotentials. Among the ten cases of TM@C9N4 considered here, only Ni@C9N4 performs as a promising bifunctional electrocatalyst with N and Ni atoms as catalytic active sites for the HER and OER, with a calculated hydrogen adsorption Gibbs free energy (ΔGH*) of -0.04 eV and an OER overpotential (ηOER) of 0.31 V. The results demonstrate that TM@C9N4 is a promising single-atom catalytic system, which can be used as the non-noble metal bifunctional electrocatalyst for overall water splitting.

Highly active single-atom catalysts (SACs) have recently been intensively studied for their potential in the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Due to the existence of many such SAC systems, a general understanding of the trend and designing principle is necessary to discover an optimal SAC system. In this work, by using density functional theory (DFT), we investigated a series of late single transition metals (TM = Fe, Co, Ni, Cu, and Pd) anchored on various N doped graphenes (xN-TM, x = 1-4) as electrocatalysts for both the HER and OER. Solvent effects were taken into account using an implicit continuum model. Our results reveal that the catalytic activity of SACs is determined by the local coordination number of N and TM in the catalysts. Among the considered catalysts, a low-coordinated Co site, i.e. a triple-coordinated Co, exhibits a high catalytic activity toward the HER with a calculated hydrogen adsorption free energy of -0.01 eV, whereas a high-coordinated Co center, i.e. a quadruple-coordinated Co is a promising candidate for the OER with a low computed overpotential of -0.39 V, which are comparable to those of noble metal catalysts, indicating superior HER and OER performance of N-Co co-doped graphenes. The results shed light on the potential applications of TM and N co-doped graphenes as efficient single-atom bifunctional catalysts for water splitting, thereby functioning as promising candidates for hydrogen/oxygen production.

Searching for highly efficient, stable and cost-effective catalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is vital to resolve energy security and environmental problems. Herein, by means of computational screening based on the density functional theory (DFT), we studied a wide range of transition metal (TM) atoms embedded into the double carbon vacancy of C3N monolayers (VCC), denoted as TM-VCC (TM = Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ir and Pt), as efficient single-atom catalysts (SACs) for OER and ORR. The calculated results showed that all the considered TM-VCC composites exhibited a metallic feature that ensured efficient charge transfer during reactions. The interaction strength between intermediates and TM-VCC has direct correlation with the d-band center of TM, which can be tuned by changing the TM atoms with different numbers of d electrons. The best catalyst for OER was Rh-VCC with an overpotential (ηOER) of 0.35 V, followed by Co-VCC (0.43 V). For the ORR process, Rh-VCC exhibited the lowest ORR overpotential (ηORR) of 0.27 V, followed by Co-VCC (0.42 V). The results suggested that the performances of the newly predicted Rh-VCC and Co-VCC SACs are comparable to those of the noble-metal benchmark catalysts for OER and ORR. Ab initio molecular dynamic simulations indicated that Rh-VCC and Co-VCC SACs could remain stable under 300 K and possessed high energy barriers to prevent the isolated Rh and Co atoms from clustering. Our results highlight a new family of efficient and stable catalysts with a single atom anchored on carbon nitride-based materials, which provides a useful guideline for catalyst design and practical applications.

The widely used density functional theory (DFT) has a major drawback of underestimating the band gaps of materials. Wannier–Koopmans method (WKM) was recently developed for band gap calculations with accuracy on a par with more complicated methods. WKM has been tested for main group covalent semiconductors, alkali halides, 2D materials, and organic crystals. Here we apply the WKM to another interesting type of material system: the transition metal (TM) oxides. TM oxides can be classified as either with d0 or d10 closed shell occupancy or partially occupied open shell configuration, and the latter is known to be strongly correlated Mott insulators. We found that, while WKM provides adequate band gaps for the d0 and d10 TM oxides, it fails to provide correct band gaps for the group with partially occupied d states. This issue is also found in other mean-field approaches like the GW calculations. We believe that the problem comes from a strong interaction between the occupied and unoccupied d-state Wannier functions in a partially occupied d-state system. We also found that, for pseudopotential calculations including deep core levels, it is necessary to remove the electron densities of these deep core levels in the Hartree and exchange–correlation energy functional when calculating the WKM correction parameters for the d-state Wannier functions.

Author(s): Liu, WH; Luo, JW; Li, SS; Wang, LW | Abstract: Photoinduced phase transitions can have complex and intriguing behaviors more than material ground-state dynamics. Understanding the underlying mechanism can help us to design new ways to manipulate the materials. A variety of mechanisms has been proposed to explain the photoinduced phase transitions of IrTe2, but a consensus has yet to be reached. Here, we study the photo-induced phase transitions of IrTe2 by performing the real-time time-dependent density functional theory (rt-TDDFT) simulations in combination with the occupation constrained DFT method. We reveal that the microscopic driving force for the photo-induced phase transitions arises from the tendency to lower the energy levels occupied by the excited carriers, through the increase or decrease of the associated atomic pair distances, depending on whether the newly occupied states are antibonding or bonding states, respectively. The geometric constraints between different bonds represented by the Poisson ratio can bring together different tendencies from different atomic pairs, thus forming a complex intriguing dynamic picture depending on the intensity of the excitation. We also find that phonons don't play a primary role, but can assist the phase transition. These findings imply that one can control the structural phase transitions by selectively exciting photocarriers into designated atomic states using appropriate photon sources.

Author(s): Singh, Y; Wang, LW | Abstract: Fully self-consistent GW (sc-GW) methods are now available to evaluate quasiparticle and spectral properties of various molecular and bulk systems. However, such techniques based on the full matrix of G and W are computationally demanding. The routinely used single-shot GW approximation (G0W0) has an undesirable dependency on the choice of initial exchange-correlation functional. In the literature, many so-called self-consistent GW methods are based on diagonal approximation of G and low-ranking approximation of W. It is thus worth checking how good such approximations are in comparison with the full matrix method. In this work, we consider AlAs, AlP, GaP, and ZnS as the prototype systems to perform sc-GW calculations by expressing the full G matrix using a plane-wave basis set. We compared our sc-GW results with the diagonal G and subspace W approximated sc-GW results (sc-GW-diagG and sc-GW-subW methods). In the sc-GW-diagG method, interacting G is expanded in the eigenvectors of noninteracting G such that only diagonal elements are retained, whereas the number of eigenmodes is truncated in sc-GW-subW calculations. A systematic analysis of the results obtained from the above techniques is presented. The differences in the quasiparticle band gap between the approximated and the full matrix sc-GW approaches are mostly less than 1.7%, which validates such widely adopted approximations, and also shows how such low-ranking approximation can be used to include higher-order terms such as the vertex correction.

Supercooled liquid sulfur provides higher capacity, faster kinetics, and better cycling life compared to solid sulfur., In lithium-sulfur (Li-S) chemistry, the electrically/ionically insulating nature of sulfur and Li2S leads to sluggish electron/ion transfer kinetics for sulfur species conversion. Sulfur and Li2S are recognized as solid at room temperature, and solid-liquid phase transitions are the limiting steps in Li-S batteries. Here, we visualize the distinct sulfur growth behaviors on Al, carbon, Ni current collectors and demonstrate that (i) liquid sulfur generated on Ni provides higher reversible capacity, faster kinetics, and better cycling life compared to solid sulfur; and (ii) Ni facilitates the phase transition (e.g., Li2S decomposition). Accordingly, light-weight, 3D Ni-based current collector is designed to control the deposition and catalytic conversion of sulfur species toward high-performance Li-S batteries. This work provides insights on the critical role of the current collector in determining the physical state of sulfur and elucidates the correlation between sulfur state and battery performance, which will advance electrode designs in high-energy Li-S batteries.

Non-adiabatic chemical reaction refers to the electronic excitation during reactions. This effect cannot be modeled by the ground-state Born–Oppenheimer molecular dynamics (BO-MD), where the electronic structure is at the ground state for every step of ions’ movement. Although the non-adiabatic effect has been explored extensively in gas phase reactions, its role in electrochemical reactions, such as water splitting and CO2 reduction, in electrolyte has been rarely explored. On the other hand, electrochemical reactions usually involve electron transport; thus, a non-adiabatic process can naturally play a significant role. In this work, using one-step CO2 reduction as an example, we investigated the role of the non-adiabatic effect in the reaction. The reaction barriers were computed by adiabatic BO-MD and non-adiabatic real-time time dependent density functional theory (rt-TDDFT). We found that by including the non-adiabatic effect, rt-TDDFT could increase the reaction barrier up to 6% compared to the BO-MD calculated barrier when the solvent model is used to represent water. Simulations were carried out using explicit water molecules around the reaction site under different overpotentials, and similar non-adiabatic effects were found.

To make a lithium-sulfur (Li-S) battery practical, not only high gravimetric energy capacity is important, but also high volumetric energy capacity will be required. The currently explored Li-S cathode designs often deploy systems with liquid electrolyte infiltration, hence with relatively low volumetric capacity. In the current study, we theoretically test a compact solid three-dimensional (3D) design (more like a Li-ion battery cathode than a conventional Li-S cathode) consisted of a sandwich structure alternating between the two-dimensional (2D) Mn-hexaaminobenzene-based coordination polymer (2D Mn-HAB-CP) layer and the amorphous Li-S layer. We study the theoretical limits for both its gravimetric and volumetric energy capacity, as well as its structural stability and Li diffusion within the cathode system. To study the Li diffusion within an amorphous system, we also develop a pull-atom molecular dynamics (PA-MD) to calculate the barrier heights of such disordered systems. We reveal the mechanism that determines the Li diffusion in the amorphous layer of the system. Overall, we find such a 3D solid Li-S cathode can be practical, with sufficient large gravimetric and volumetric energy capacity, as well as the Li diffusion constant. It also solves many other common Li-S cathode problems, from Li polysulfide dissolution to electrical insulating, and structure instabilities.

Charged-defect calculation using a periodic supercell is a significant class of problems in solid state physics. However, the finite supercell size induces an undesirable long-range image charge Coulomb interaction. Although a variety of methods have been proposed to eliminate such image Coulomb interaction, most of the previous schemes are based on a rough approximation of the defect charge screening. In this work, we present a rigorous derivation of the image charge interaction with a new defect screening model where the use of bulk macroscopic dielectric constant can be avoided. We have verified this approach in comparison with a widely used approach for 12 different defects. Our correction scheme offers a much faster convergence concerning the supercell size for cases with considerable image charge interactions. In those cases, we also found that the nonlinear dielectric screening might play an important role. The proposed new defect screening model will also shed new light on understanding the defect screening properties and can be applied to other defect systems.

Heat-induced perovskite LED device degradation is elucidated via insightful in situ structure and spectroscopy characterizations., Achieving perovskite-based high–color purity blue-emitting light-emitting diodes (LEDs) is still challenging. Here, we report successful synthesis of a series of blue-emissive two-dimensional Ruddlesden-Popper phase single crystals and their high–color purity blue-emitting LED demonstrations. Although this approach successfully achieves a series of bandgap emissions based on the different layer thicknesses, it still suffers from a conventional temperature-induced device degradation mechanism during high-voltage operations. To understand the underlying mechanism, we further elucidate temperature-induced device degradation by investigating the crystal structural and spectral evolution dynamics via in situ temperature-dependent single-crystal x-ray diffraction, photoluminescence (PL) characterization, and density functional theory calculation. The PL peak becomes asymmetrically broadened with a marked intensity decay, as temperature increases owing to [PbBr6]4− octahedra tilting and the organic chain disordering, which results in bandgap decrease. This study indicates that careful heat management under LED operation is a key factor to maintain the sharp and intense emission.

An understanding of nanocrystal shape evolution is significant for the design, synthesis, and applications of nanocrystals with surface-enhanced properties such as catalysis or plasmonics. Surface adsorbates that are selectively attached to certain facets may strongly affect the atomic pathways of nanocrystal shape development. However, it is a great challenge to directly observe such dynamic processes in situ with a high spatial resolution. Here, we report the anomalous shape evolution of Ag2O2 nanocrystals modulated by the surface adsorbates of Ag clusters during electron beam etching, which is revealed through in situ transmission electron microscopy (TEM). In contrast to the Ag2O2 nanocrystals without adsorbates, which display the near-equilibrium shape throughout the etching process, Ag2O2 nanocrystals with Ag surface adsorbates show distinct facet development during etching by electron beam irradiation. Three stages of shape changes are observed: a sphere-to-a cube transformation, side etching of a cuboid, and bottom etching underneath the surface adsorbates. We find that the Ag adsorbates modify the Ag2O2 nanocrystal surface configuration by selectively capping the junction between two neighboring facets. They prevent the edge atoms from being etched away and block the diffusion path of surface atoms. Our findings provide critical insights into the modulatory function of surface adsorbates on the shape control of nanocrystals.

We introduce a general surface passivation mechanism for cesium lead halide perovskite materials (CsPbX3, X = Cl, Br, I) that is supported by a combined experimental and theoretical study of the nanocrystal surface chemistry. A variety of spectroscopic methods are employed together with ab initio calculations to identify surface halide vacancies as the predominant source of charge trapping. The number of surface traps per nanocrystal is quantified by 1H NMR spectroscopy, and that number is consistent with a simple trapping model in which surface halide vacancies create deleterious under-coordinated lead atoms. These halide vacancies exhibit trapping behavior that differs among CsPbCl3, CsPbBr3, and CsPbI3. Ab initio calculations suggest that introduction of anionic X-type ligands can produce trap-free band gaps by altering the energetics of lead-based defect levels. General rules for selecting effective passivating ligand pairs are introduced by considering established principles of coordination chemistry. Introducing softer, anionic, X-type Lewis bases that target under-coordinated lead atoms results in absolute quantum yields approaching unity and monoexponential luminescence decay kinetics, thereby indicating full trap passivation. This work provides a systematic framework for preparing highly luminescent CsPbX3 nanocrystals with variable compositions and dimensionalities, thereby improving the fundamental understanding of these materials and informing future synthetic and post-synthetic efforts toward trap-free CsPbX3 nanocrystals.

Summary Aqueous electrolytes come with an intrinsic narrow electrochemical stability window (1.23 V). Expanding this window represents significant benefits in both fundamental science and practical battery applications. Recent breakthroughs made via super-concentration have resulted in >3.0 V windows, but fundamental understanding of the related mechanism is still absent. In the present work, we examined the widened window (2.55 V) of a super-concentrated (unsaturated) aqueous solution of LiNO3 through both theoretical and spectral analyses and discovered that a local structure of intimate Li+-water interaction arises at super-concentration, generating (Li+(H2O)2)n polymer-like chains to replace the ubiquitous hydrogen bonding between water molecules. Such structure is mainly responsible for the expanded electrochemical stability window. Further theoretical and experimental analyses quantitatively differentiate the contributions to this window, identifying the kinetic factor (desolvation) as the main contributor. Such molecular-level and quantitative understanding will further assist in tailor designing more effective approaches to stabilizing water electrochemically.

Recent experiments have shown that CO reduction on oxide derived Cu nanoparticles (NP) are highly selective toward C2+ products. However, understanding of the active sites on such NPs is limited, because the NPs have ∼200 000 atoms with more than 10 000 surface sites, far too many for direct quantum mechanical calculations and experimental identifications. We show here how to overcome the computational limitation by combining multiple levels of theoretical computations with machine learning. This approach allows us to map the machine learned CO adsorption energies on the surface of the copper nanoparticle to construct the active site visualization (ASV). Furthermore, we identify the structural criteria for optimizing selective reduction by predicting the reaction energies of the potential determining step, ΔEOCCOH, for the C2+ product. Based on this structural criterion, we design a new periodic copper structure for CO reduction with a theoretical faradaic efficiency of 97%.

We use ab initio calculations to explore the geometry, bonding and electronic properties of Mxene/blue phosphorene (BLP) heterobilayers. Perfect lattice-matched and energetically stable Mxene/BLP heterobilayers are firstly predicted to be vertically stacked with less than 1% lattice mismatch. The electronic properties of the heterobilayers are consistent with the substrate Mxene and the states projected on the isolated components are preserved. The unchanged electronic properties for the components upon the formation of the heterobilayers indicate the physical vdW interaction between the BLP monolayers and Mxene sheet, instead of the chemical bonds. The most stable BLP/Y2CX2 (X = O, and Y = Hf, Zr) are found to be a semiconductor with a type-II band alignment where the excited electrons and holes are localized in different layers. However, for BLP/Y2CX2 (X = F, and Y = Hf, Zr), the most stable structure is metallic with a strong band bending which lead to the existence of a partial flat band along the Γ point to the M point that mainly originates from the BLP monolayes. The appearance of the spatial separation of electron and hole and the partial flat band in these heterostructures have potential applications in optoelectronic devices and strong electron-electron correlation field. Our analysis also suggests that Mxene is a promising substrate to grow BLP monolayer epitaxially.

Two-dimensional transition metal dichalcogenides have attracted intense interests in recent years. Existing studies have fully explored the properties of their ground-state structures, but their global energy landscapes are still not well understood. The global energy landscape is important for understanding the experimental synthesis and thermal dynamic properties as well as for discovering new phases. This work uses material genome techniques (huge global search and data mining) to explore the global energy landscapes and new phases of two-dimensional MoS2, WS2, and ReS2 monolayers at ab initio level. Our results show that their energy landscapes have two or three major funnels, each of which consists of a few local minima with hexagonal, octahedral, quadrilateral, nanoribbon structures as well as their distorted and hybrid structures. The global-minimum structures are confined in deep funnels while the higher-energy minima stay in flat funnels and can transform to other minima at high temperatures. A f...

Utilizing Pt nanoparticles of varying sizes (2–7 nm), it was found that the oxidation of 1-propanol by molecular oxygen at 60 °C to propanal at the solid–gas and solid–liquid interfaces yielded significantly different results depending on Pt particle size and alcohol surface density. The reaction rate at the solid–gas interface was found to be 1 order of magnitude greater than that at the solid–liquid interface after normalizing concentration. In addition, catalytic activity increases with the size of Pt nanoparticles for both reactions. Moreover, water substantially promoted 1-propanol oxidation in the liquid phase, yet it inhibited the reaction in the gas phase. The gas phase and liquid phase reactions are believed to undergo different mechanisms due to differing kinetic results. This correlated well with different orientations of the 1-propanol species at the solid–gas interface versus the solid–liquid interface as probed by sum–frequency generation vibrational spectroscopy (SFGVS) under reaction condi...

One of the biggest challenges of Li–S batteries (LSBs) is the dissolution of polysulfides at the cathode side. An ideal LSB cathode should be able to prevent polysulfide (Li2Sn, 1 ≤ n ≤ 8) dissolution, and should have a strong binding energy, high capacity and a light weight, as well as being electrically conductive. Herein, we present our quantum chemical calculations combined with a genetic algorithm for a global structure search using a C2N nanosheet as a LSB cathode. The Gibbs free energies of isolated Li2Sn and LimSn_C2N (1 ≤ m, 1 ≤ n ≤ 8) are calculated to set forth the studies of both the voltages and stabilities of lithiation reactions in every step of the discharging process. Our results indicate that the polysulfides can adhere to the C2N host substrate in a thermodynamically stable cluster state without dissolution, and the system has an energy capacity of up to 1122.21 W h kg−1. The calculated band-structure shows that LimSn_C2N is metallic though the original C2N nanosheet has an optical gap of 1.96 eV. This shows that C2N could be a promising cathode material for LSBs.

A new type of two-dimensional (2D) material, phosphorene oxides (POs) in four surface oxidation states (P4O1, P4O2, P4O3 and P4O4), is evaluated as a potential cathode for sealed Li–oxygen batteries by combining the first-principles method with molecular dynamics simulations and implicit solvent models. The system can be sealed because, unlike open Li–air batteries, there is no need to take oxygen from air. Our simulations reveal that: (1) by forming a maximum number of Li–O bonds, Li can be tightly chemisorbed on the surface of POs with a large binding energy ranging from −2.32 to −3.72 eV and a charge transfer of ∼0.9e from Li to O. (2) The diffusion of Li on POs is strongly anisotropic as the barrier along the armchair direction is nearly two times higher than that along the zigzag direction. The barrier dramatically decreases to 0.2 eV with increasing oxidation, indicating a high diffusivity. (3) For the P4O4 cathode, the thermodynamically stable, fully discharged product has a stoichiometry of Li : P : O = 1 : 1 : 1, achieving a specific capacity of 570.56 mA h g−1, an average open-circuit voltage of 2.55 V and an energy density of 1457 W h kg−1. The energy density can be further increased by considering solvent effects. More polar cyclic ethylene carbonate (EC) solvent brings about a larger energy density enhancement than less polar linear 1,2-dimethoxyethane (DME). (4) Semiconductor-to-metal transition occurs within POs after Li adsorption, facilitating the electrical transport in PO-based batteries. A combination of strong Li adsorption, high diffusivity, and good conductivity makes POs great candidates for future fully sealed Li–oxygen batteries.

β-Ga2O3 has drawn recent attention as a state-of-the-art electronic material due to its stability, optical transparency and appealing performance in power devices. However, it has also found a wider range of opto-electronic applications including photocatalysis, especially in its porous form. For such applications, a lower band gap must be obtained and an electron-hole spatial separation would be beneficial. Like many other metal oxides (e.g. Al2O3), Ga2O3 can also form various types of porous structure. In the present study, we investigate how its optical and electronic properties can be changed in a particular porous structure with stoichiometrically balanced and extended vacancy channels. We apply a set of first principles computational methods to investigate the formation and the structural, dynamic, and opto-electronic properties. We find that such an extended vacancy channel is mechanically stable and has relatively low formation energy. We also find that this results in a spatial separation of the electron and hole, forming a long-lived charge transfer state that has desirable characteristics for a photocatalyst. In addition, the electronic band gap reduces to the vis-region unlike the transparency in the pure β-Ga2O3 crystal. Thus, our systematic study is promising for the application of such a porous structure of β-Ga2O3 as a versatile electronic material.

Water splitting to generate hydrogen and oxygen gas is critical to renewable energy technologies, including fuel cells and rechargeable metal–air batteries. The oxygen evolution reaction (OER) has long been the bottleneck of water splitting because of its high overpotential (η) and sluggish kinetics, and development of efficient, stable, and non-noble-metal-based OER catalysts has been an extensively studied topic. Here, we propose short hydrogen bonds on reconstructed nanocrystal surface to enhance oxygen evolution activity by investigating three types of phase structures (βII, βI, and γ0) of Li2CoSiO4 (LCS) nanoparticles as OER electrocatalysts. Among them, the βII-LCS outperforms the previously reported Co-based catalysts and the state-of-the-art IrO2 catalyst for OER in the alkaline condition. Our experiments combined with ab initio calculations indicated that due to the line-linked arrangement of Co active sites at the surface of βII-LCS, short hydrogen bonds (2.54 A) are formed and linked into a net...

As the high throughout calculations and material genome approaches become more and more popular in material science, the search for optimal ways to predict atomic global minimum structure is a high research priority. This paper presents a fast method for global search of atomic structures at ab initio level. The structures global optimization (SGO) engine consists of a high-efficiency differential evolution algorithm, accelerated local relaxation methods and a plane-wave density functional theory code running on GPU machines. The purpose is to show what can be achieved by combining the superior algorithms at the different levels of the searching scheme. SGO can search the global-minimum configurations of crystals, two-dimensional materials and quantum clusters without prior symmetry restriction in a relatively short time (half or several hours for systems with less than 25 atoms), thus making such a task a routine calculation. Comparisons with other existing methods such as minima hopping and genetic algorithm are provided. One motivation of our study is to investigate the properties of magnetic systems in different phases. The SGO engine is capable of surveying the local minima surrounding the global minimum, which provides the information for the overall energy landscape of a given system. Using this capability we have found several new configurations for testing systems, explored their energy landscape, and demonstrated that the magnetic moment of metal clusters fluctuates strongly in different local minima.

CH3NH3PbI3 is one of the most promising candidates for cheap and high-efficiency solar cells. One of its unique features is the long carrier diffusion length (>100 μm), but its carrier mobility is rather modest. The nature of the mobility is unclear. Here, using nonadiabatic wave function dynamics simulations, we show that the random rotations of the CH3NH3 cations play an important role in the carrier mobility. Our previous work showed that the electron and hole wave functions were localized and spatially separated due to the random orientations of the CH3NH3 cations in the tetragonal phase. We find that the localized carriers are able to conduct random walks due to the electrostatic potential fluctuation caused by the CH3NH3 random rotations. The calculated electron mobilities are in the experimentally measured range. We thus conclude that the carrier mobility of CH3NH3PbI3 is likely driven by the dynamic disorder that causes the fluctuation of the electrostatic potential.

Pt nanoclusters play an important role in catalysis-related applications. Essential to their activities are their geometries and energy landscapes. In this work, we studied the energy landscapes of Pt clusters using a parallel differential evolution optimization algorithm and an accelerated ab initio atomic relaxation method, which allowed us to explore unprecedentedly large numbers of geometry local minima at ab initio level. We found many lower-energy isomers with low symmetry in their geometry. The energy landscapes were demonstrated to be glass-like with a large number of local minimum structures close to the global minimum. The electronic and magnetic properties of most glass-like local minima were dramatically different from the global minimum, and they should be observed in the experimental measurements. The connections between these local minima were further analyzed using data mining techniques.

LS3DF, namely linear scaling three-dimensional fragment method, is an efficient linear scaling ab initio total energy electronic structure calculation code based on a divide-and-conquer strategy. In this paper, we present our GPU implementation of the LS3DF code. Our test results show that the GPU code can calculate systems with about ten thousand atoms fully self-consistently in the order of 10 min using thousands of computing nodes. This makes the electronic structure calculations of 10,000-atom nanosystems routine work. This speed is 4.5–6 times faster than the CPU calculations using the same number of nodes on the Titan machine in the Oak Ridge leadership computing facility (OLCF). Such speedup is achieved by (a) carefully re-designing of the computationally heavy kernels; (b) redesign of the communication pattern for heterogeneous supercomputers .

The formation energies and charge-transition levels of intrinsic point defects in lead halide perovskite CsPbBr3 are studied from first-principles calculations. It is shown that the formation energy of dominant defect under Br-rich growth condition is much lower than that under moderate or Br-poor conditions. Thus avoiding the Br-rich condition can help to reduce the defect concentration. Interestingly, CsPbBr3 is found to be highly defect-tolerant in terms of its electronic structure. Most of the intrinsic defects induce shallow transition levels. Only a few defects with high formation energies can create deep transition levels. Therefore, CsPbBr3 can maintain its good electronic quality despite the presence of defects. Such defect tolerance feature can be attributed to the lacking of bonding-antibonding interaction between the conduction bands and valence bands.

The crystalline-Si/amorphous-SiO2 (c-Si/a-SiO2) interface is an important system used in many applications, ranging from transistors to solar cells. The transition region of the c-Si/a-SiO2 interface plays a critical role in determining the band alignment between the two regions. However, the question of how this interface band offset is affected by the transition region thickness and its local atomic arrangement is yet to be fully investigated. Here, by controlling the parameters of the classical Monte Carlo bond switching algorithm, we have generated the atomic structures of the interfaces with various thicknesses, as well as containing Si at different oxidation states. A hybrid functional method, as shown by our calculations to reproduce the GW and experimental results for bulk Si and SiO2, was used to calculate the electronic structure of the heterojunction. This allowed us to study the correlation between the interface band characterization and its atomic structures. We found that although the systems with different thicknesses showed quite different atomic structures near the transition region, the calculated band offset tended to be the same, unaffected by the details of the interfacial structure. Our band offset calculation agrees well with the experimental measurements. This robustness of the interfacial electronic structure to its interfacial atomic details could be another reason for the success of the c-Si/a-SiO2 interface in Si-based electronic applications. Nevertheless, when a reactive force field is used to generate the a-SiO2 and c-Si/a-SiO2 interfaces, the band offset significantly deviates from the experimental values by about 1 eV.

Author(s): Liu, YY; Liu, F; Wang, R; Luo, JW; Jiang, X; Huang, R; Li, SS; Wang, LW | Abstract: The complexity of charge trapping in semiconductor devices, such as high-κ MOSFETs, is increasing as the devices themselves become more complicated. To facilitate research into such charge-trapping issues, here we propose an optimized simulation framework that is composed of density-functional theory (DFT) for electronic structure calculation and Marcus theory for the calculation of charge-trapping rates. The DFT simulations are either carried out or corrected by using the Heyd-Scuseria-Ernzerhof hybrid functional. Using this framework, the hole-trapping characteristics along multiple paths in Si/SiO2/HfO2 stacks are investigated, and the relative importance of each path is revealed by calculating its exact hole-trapping rate. Besides the study on crystalline stacks, we also create an amorphous stack, which is more realistic compared with experiments and real devices, to reveal more active trapping centers and to study the statistical feature of charge trapping induced by structural disorder. In addition, to seek effective measures for relieving these charge-trapping problems, the effects of hydrogen and fluorine passivations are discussed, and physical insights for improving the performance of high-κ MOSFETs are provided.

Low-energy impurity diffusion in a host material is often regarded as an adiabatic process, characterized by its adiabatic potential energy barrier. Here we show that the diffusion process in semiconductors can involve nonadiabatic electron excitations, rending it to be a more complicated process. Impurity diffusion in a device at working temperature can pump one electron up from localized impurity state into the host conduction band and causes the impurity to be a dynamic donor since it temporarily loses its electron to the host. This nonadiabatic process, against a common belief, fundamentally change the diffusion behavior, including its barrier height and diffusion path. Although we mainly demonstrate this process with Au metal impurity in bulk Si through time-dependent density functional theory simulations, we believe this could be a rather common phenomenon as it is shown that the similar phenomena also exist in Zn, Cd impurities diffusion in bulk Si, and Ti diffusion in $\mathrm{Ti}{\mathrm{O}}_{2}$. We believe this study can open up a new direction of inquiry for such diffusion behavior in semiconductor.

Plasmon photochemistry can potentially play a significant role in photocatalysis. To realize this potential, it is critical to enhance the plasmon excited hot carrier transfer and collection. However, the lack of atomistic understanding of the carrier transfer across the interface, especially when the carrier is still "hot", makes it challenging to design a more efficient system. In this work, we apply the nonadiabatic molecular dynamics simulation to study hot carrier dynamics in the system of a Au nanocluster on top of a GaN surface. By setting up the initial excited hole in Au, the carrier transfer from Au to GaN is found to be on a subpicosecond time scale. The hot hole first cools to the band edge of Au d-states while it transfers to GaN. After the hole has cooled down to the band edge of GaN, we find that some of the charges can return back to Au. By applying different external potentials to mimic the Schottky barrier band bending, the returning charge can be reduced, demonstrating the importance of the internal electric field. Finally, with the understanding of the carrier transfer's pathway, we suggest that a ZnO layer between GaN and Au can effectively block the "cold" carrier from returning back to Au but still allow the hot carrier to transfer from Au to GaN.

The condensation of half-light half-matter exciton polaritons in semiconductor optical cavities is a striking example of macroscopic quantum coherence in a solid state platform. Quantum coherence is possible only when there are strong interactions between the exciton polaritons provided by their excitonic constituents. Rydberg excitons with high principle value exhibit strong dipole-dipole interactions in cold atoms. However, polaritons with the excitonic constituent that is an excited state, namely Rydberg exciton polaritons (REPs), have not yet been experimentally observed. Here, for the first time, we observe the formation of REPs in a single crystal CsPbBr3 perovskite cavity without any external fields. These polaritons exhibit strong nonlinear behavior that leads to a coherent polariton condensate with a prominent blue shift. Furthermore, the REPs in CsPbBr3 are highly anisotropic and have a large extinction ratio, arising from the perovskite's orthorhombic crystal structure. Our observation not only sheds light on the importance of many-body physics in coherent polariton systems involving higher-order excited states, but also paves the way for exploring these coherent interactions for solid state quantum optical information processing.