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Abstract: We investigate the multilayer relaxation trends in the vicinal Cu(p,p,p −2) surfaces employing the all-electron full-potential linearized augmented plane-wave method. Calculations are performed for the (331), (221), (553), (332), (775), and (443) surfaces, which have 3, 4, 5, 6, 7, and 8 atom-rows in the terrace, respectively. The following trends are identified: (i) The interlayer relaxations perpendicular to the surface scale almost linearly with the number of atom-rows in the terraces. (ii) The nearest-neighbor distances do not depend on the surface termination, but only on the local coordination. (iii) For Cu(p,p,p −2) in which the topmost n surface layers have nearest-neighbor coordination smaller than the bulk Cu (calculated for the unrelaxed surfaces), the topmost (n −1) interlayer spacings (d 12,…, d n−1,n ) contract compared with the unrelaxed spacing, while the nth interlayer spacing (d n,n+1) expands. The next (n −2) interlayer spacings (d n+1,n+2,…, d 2n−2,2n−1) contract, while the interlayer spacing indicated by d 2n−1,2n expands. A similar rule was found for the relaxations parallel to the surfaces. These trends provide a better understanding of the atomic structure of vicinal Cu surfaces. [Copyright &y& Elsevier]

MoS2 nanoflakes have attracted wide attention due to their outstanding catalytic activity induced by their active zigzag edges. Nanoflakes morphologies dictate their electronic properties, and factors such as size, doping, and interaction with a substrate determines their behavior. Herein, we investigate the role of the Au(111) substrate in the morphology of Mo10S24 nanoflakes via first-principles density functional theory calculations combined with the k-means clustering algorithm for structure selection. From our initial calculations for gas-phase nanoflakes, we found that asymmetric morphologies are about 2.7 eV lower in energy than the symmetric ones. Thus, we deposited a few nanoflakes on the Au(111) substrate to investigate their effects. Here, we obtain a strong nanoflake/gold interaction ruled by features such as symmetry, roughness, and vertical S – Au stacking. The S – Au interaction is large enough to change the relative energies between the nanoflakes in the gas-phase by more than 2.0 eV, which indicates the relevance of substrate engineering for the nanoflake morphology. • Asymmetric nanoflakes in the gas phase have total energies lower than symmetric ones. • S–Au coordination, and roughness rules the nanoflake/Au(111) interaction. • The work function remains almost constant after the nanoflake adsorption. • The morphology of nanoflakes on gold surfaces depends on the synthesis route. [ABSTRACT FROM AUTHOR]

Deep eutectic solvents (DES), such as the ▪:▪ (sodium bistrifluoromethane sulfonyl imide - N-methyl acetamide) system, have been considered as promising electrolytes for sodium-ion (▪) batteries. However, our current atomistic understanding of those systems is still in a state of evolution and remains incomplete. In this context, we combined classical force field molecular dynamics (MD) simulations and periodic density functional theory (DFT) calculations to enhance our atomistic understanding on the ▪ transport mechanisms, DES structure organization, hydrogen-bond network formation, and electrochemical stability windows (ESWs). Firstly, we obtained a substantial improvement in the description of the DES transport and structural properties using self-consistent MD/DFT calculations to assign effective charges on all atoms, while the remaining OPLS parameters were kept constant. From our analyses, an increasing in the ▪ mole fraction leads to different chemical environments, reflecting an electrolyte with larger aggregates, low conductivity, and high viscosity. The liquid structure seems to remain unchanged as a function of temperature. However, higher temperatures reduce the lifetime of ionic pairs and increase the mobility of ▪ ions. The disruption of the hydrogen-bonds formed between the ▪ species increases with the ▪ concentration. In addition, our periodic DFT calculations reveals the substitution of atomic sites from ▪ to ▪ during the reduction process. Furthermore, the ESW results provided evidence supporting the safeguarding of the solvent from degradation at higher salt concentrations. • Investigation of ▪:▪ DES employing a self-consistent MD/DFT charge model alongside OPLS-AA force field. • Higher ▪ mole fraction results in stable, low-conductivity, high-viscosity electrolyte environments. • Elevated temperature enhances ▪ mobility by softening ionic interactions. • Observation of strong ionic interactions among ▪ coupled with hydrogen bond breaking. • Periodic DFT calculations were employed to address electrochemical stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ultrasound, microwave and autoclave were tested in the synthesis of hydroxyapatite. • The post-synthesis treatments changed the acid/basic profile on the solid surface. • The microwave-treated catalyst had the best results in the ethanol condensation. • Basic surface sites decreased intrinsic activation energies. • Balanced distribution of acidic/basic sites accelerates aldol condensation. Several studies have investigated the acidic/basic sites of the hydroxyapatite (HAP) surface. However, their specific role in the catalytic properties of HAP is still discussed. Here, we investigated different preparation methods (ultrasound, microwave, and autoclave) of HAP and how they affect the catalytic activity for ethanol conversion. The synthesis methods changed the number and distribution of acidic/basic sites, affecting the product selectivity. The best performance toward condensation products was observed for the microwave-treated catalyst. We also report a density functional theory (DFT) investigation on the reaction pathways of twelve steps of ethanol conversion on the HAP(0001) surface. Our DFT results suggest that the availability of basic sites can facilitate acetaldehyde formation. Furthermore, our theoretical insights indicate that the balance of acidic/basic sites contributes to the C−C bond formation, which is consistent with our experimental observations. [ABSTRACT FROM AUTHOR]

• Ab-initio Sn 3 O 4 exfoliation energy lies in the van der Waals layered materials range. • A modern Scotch-tape exfoliation of a Sn 3 O 4 nanobelt carried out using a Dual Beam Microscope. • As predicted theoretically, a few layers from Sn 3 O 4 nanobelt could be exfoliated. • Using the same nanomanipulation, layers could not be removed from the SnO and SnO 2. Van der Waals (vdW) layered materials have been receiving a great deal of attention, especially after the scotch-tape experiment using graphite and the unique properties of graphene. Sn 3 O 4 , which also presents a layered structure, has been widely employed in a variety of technologies, but without further understanding of its bulk properties. For the first time, a modern Scotch-tape nanomanipulation experiment carried on a Dual Beam Microscope is combined with Density Functional Theory to investigate the Sn 3 O 4 bulk properties. Theoretically, we have shown that the interaction energy between Sn 3 O 4 layers are in the same order of graphene layers (21 meV Å−2), indicating its vdW interaction nature, whereas for SnO is slightly stronger (26 meV Å−2). Then, the Dual Beam Microscope nanomanipulation of the Sn 3 O 4 nanobelts revealed the weak layer-layer interactions along their stacking direction (plane (0 1 0)). Comparatively, when probing SnO and SnO 2 nanobelts, no exfoliation could be seen. The study of Sn 3 O 4 electronic structure properties also presents the important role of the interfacial region to the valence and conduction band and, consequently, to the material band-gap. The outcome of this study will help improving some applications, e.g., knowing the total and local density of states can help understanding surface band bending following gases adsorption. To the best of our knowledge, this is the first study to show, combining experimental and theoretical techniques, Sn 3 O 4 as a promising 2D material. [ABSTRACT FROM AUTHOR]

Platinum (Pt) atoms in the bulk face-centered cubic structure have neutral charge because they are equivalent by symmetry, however, in clean Pt surfaces, the effective charge on Pt atoms can turn slightly negative (anionic) or positive (cationic) while increasing substantially in magnitude for defected (low-coordinated) Pt sites. The effective charge affect the adsorption properties of molecular species on Pt surfaces and it can compete in importance with the coupling of the substrate-molecule electronic states. Although several studies have been reported due to the importance of Pt for catalysis, our understanding of the role played by low-coordinated sites is still limited. Here, we employ density functional theory within the Perdew–Burke–Ernzerhof exchange-correlation functional and the D3 van der Waals (vdW) correction to investigate the role of the cationic and anionic Pt sites on the adsorption properties of ethanol and water on defected Pt 4 /Pt(111) substrates. Four substrates were carefully selected, namely, two two-dimensional (2D) Pt 4 configurations (2D-strand and 2D-island) and two tri-dimensional (3D) Pt 4 (3D-fcc and 3D-hcp), to understand the role of coordination, effective charge, and coupling of the electronic states in the adsorption properties. From the Bader charge analysis, we identified the cationic and anionic sites among the Pt atoms exposed to the vacuum region in the Pt 4 /Pt(111) substrates. We found that ethanol and water bind via the anionic O atoms to the low-coordinated defected Pt sites of the substrates, where the angle PtOH is nearly 100° for most configurations. In the 3D-fcc or 3D-hcp defected configurations, the lowest-coordinated Pt atoms are anionic, hence, those Pt sites are not preferable for the adsorption of O atoms. The charge transfer from water and ethanol to the Pt substrates has similar magnitude for all cases, which implies similar Coulomb contribution to the adsorption energy. Moreover, we found a correlation of the adsorption energy with the shift of the center of gravity of the occupied d -states of Pt sites. [ABSTRACT FROM AUTHOR]

The search and characterization of Weyl Semimetals (WSMs) is a challenge, in particular, because it requires a deep numerical analysis of the Fermi surface to identify the Fermi arcs. Here, we proposed a theoretical framework based on the combination of density functional theory with maximally localized Wannier functions for tight-binding parametrization and topological analyses to identify and characterize WSMs compounds. Inspired by the results reported for the transition-metal dichalcogenides (TMDs) compounds, namely, the WTe 2 and MoTe 2 systems, we selected the layered Janus-TMDs M TeSe (M = W, Mo, Cr) compounds in the 1 T , 1 T ′ , and 1 T d structures to search for new WSMs. Based on phonons calculations, we found that only 8 Janus-TMDs are stable. The stacking 3D structure of the Janus-TMDs reveals a strong k z Fermi surface dependence. We report different Fermi surface k -planes behavior: (i) a point-like kind and (i i) a non-point like that are related to a cone and a tilted cone energy dispersion, respectively. From our results, we introduced a sub-classification inside the previous type II WSMs, namely, (i) strong type II if all Fermi surface k -planes present non-point like behavior and (i i) weak type II if one plane is point-like. As before, all planes with point-like Fermi surface stands for type I. Based on that, only one Janus-TMDs was found to be of type I, while the remaining systems are separated into two groups, namely, weak and strong type II. From our understanding, the planar Hall current experiments might be sensitive and able to distinguish the two sub-type II classification. From our calculations and analyses, the Janus structures exhibit Weyl points with a large separation in k -space compared with the pristine ones. This property is fundamental to obtain large extended Fermi arcs on the surface of the material and design good candidates for angle-resolved photoemission spectroscopy experiments. [Display omitted] • We studied the stability and topological phases of TMD Janus configurations. • We investigate a total of 27 systems,9 TMDs and 18 Janus-TMDs. • We found a new family of Topological Janus structures based on Cr. • We found large Fermi arcs on the surface of the CrTeSe-XX 1Td materials. • We proposed a new subclassification for type II Janus Weyl semimetals. [ABSTRACT FROM AUTHOR]

[Display omitted] • N,S co-doped carbonaceous shell coordinated Ru nanoclusters are synthesized. • Strong interaction between the components regulates the local coordination environment of the Ru/NSC catalyst. • Low loading of Ru nanoclusters (2.58 wt%) exhibits 50 and 110 mV overpotentials in 1 M KOH and 1 KHCO 3. • The upshift of d -band center for Ru atoms optimizes the water and hydrogen adsorption energies. Exploring effective electrocatalyst with low-cost for hydrogen evolution reaction (HER) is highly desirable for commercial hydrogen production. Herein, a heterogeneous nanostructured catalyst is synthesized by implanting Ru nanoclusters into N and S co-doped carbonaceous shell using a simple thermal condensation of glucose and thiourea with ruthenium chloride precursors followed by carbonization. Due to the unique structural design and synergistic effect of Ru nanoclusters embedded in N, S co-doped carbonaceous shell (NSC), the compositionally tuned catalyst (Ru/NSC-200) tends to show HER activity with overpotentials of 50 and 110 mV at 10 mA cm−2 current density in 1 M KOH and 1 M KHCO 3 solutions, respectively. The catalyst exhibits mass activity of 10- and 1.2-times greater than those of commercial Pt/C (20 wt%) in 1 M KOH and 0.5 M H 2 SO 4 solutions, which reveals the techno-economic trait of the catalyst. Density functional theory (DFT) calculations demonstrate that the NSC induces a strong interaction with Ru, facilitating fast electron transfer during the catalysis. This work provides a simple and straightforward approach to develop effective catalyst in the realm of hydrogen evolution reaction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fluoroalkoxyaluminate anion size and charge distribution weaken Na+[anion] pair. • The weak Na+[anion] pair decreases its lifetime improving Na+ transport. • Fluoroalkoxyaluminate anion-based electrolytes present a wide electrochemical window. Ionic liquids (ILs) are a promising class of materials because of their unique properties such as high electrochemical stability window and intrinsic conductive nature, which are desirable in the development of high-performance electrolytes for energy storage applications. However, the strong Coulombic interactions between cation and anion, which contributes to the high viscosity of the ILs, are the main bottleneck in their applications as electrolytes. Weakly coordinated anions-based ILs are a class of electrolytes with high degree of charge delocalization, which leads to weak ionic interactions and improves the ionic transport. Here, we have performed molecular dynamics simulations and density functional theory calculations of imidazolium and ammonium-based ionic liquids in different Na+ mole fractions comprising the weakly coordinated fluoroalkoxyaluminate anion ([Al(Ohfip) 4 ]−). The results have shown that the 0.8-scaled OPLS-AA based force field predicted the transport properties of neat systems with good accuracy. The Na+-[anion] pair structural and lifetime analysis suggest that the fluoroalkoxyaluminate promotes lower lifetimes and facilitates the mobility of Na+ in these systems. Although the cations provided similar transport and structural results for Na+, the theoretical electrochemical stability windows of the ammonium-derived ILs exhibited values above 5.0 eV, which indicates good performance for energy storage applications. [ABSTRACT FROM AUTHOR]

Nanoalloys have been investigated for a wide range of applications, however, our atomistic understanding of the physical-chemistry properties is still far from complete as quantum-size effects play an important role for particles with about 1 nm diameter. In this work, we employed density functional theory calculations to investigate the structural, energetic and electronic properties of 55-atom A 55- n B n nanoalloys, where A , B = Al, Cu, Zn, and Ag. For structure generation, we combined clustering algorithm techniques with design principles, which yields a wide range of conformations. From the analyses of the excess energy results, we found that the CuAl, CuAg, CuZn, and AlAg systems are the most energetically favorable, in particular, the Al 42 Cu 13 and Al 42 Ag 13 compositions (onion-like and core–shell structures, respectively). Through Spearman's correlation analysis, we found that the structural properties (number of under coordinated atoms, effective coordination number, average bond lengths, and chemical order parameter) are the most important descriptors correlated with the energy stability of the nanoalloys (excess energy). Several properties such as the particle volume, binding energy, and average bond length show a linear dependence as a function of composition. [ABSTRACT FROM AUTHOR]

Binary transition-metal clusters have attracted great attention and a large number of studies have been reported, however, our atomistic understanding of the structural formation mechanisms of those clusters is still far from satisfactory. In this paper, we report a systematic study of the Pt n Cu m − n clusters ( m = 2 , 3 , … , 14 , n = 0 , 1 , … , m ) employing Ab-Initio density functional theory calculations within the Perdew–Burke–Ernzerhof functional. Using a set of structural design principles, we obtained a hierarchical set of atomic configurations from which the structural formation mechanisms are discussed in details. We found a negative excess energy for m > 2 , providing strong evidence favouring the formation of binary PtCu clusters. In general, the Cu atoms tend to form agglomerates located near the center of gravity of the clusters while the Pt atoms tend to lie further away from the center of gravity and separated from each other. Therefore, this behaviour tends to reduce the number of Pt–Pt bonds whereas the number of Cu–Cu and Pt–Cu bonds tends to be maximized. These mechanisms help to release strain energy by means of relaxation of the gas-phase clusters, and the locations of the Cu and Pt atoms suggest that the formation of core–shell like structures starts already in this small size regime. Furthermore, the formation of the PtCu alloy does not lead to changes in the magnetic properties of the clusters in comparison with the parent Pt and Cu clusters. The systematic work presented here provides a basis to understand and tailor the properties of binary cluster. [ABSTRACT FROM AUTHOR]

Supported Ni-Ga alloys have emerged as potential catalyst to mitigate CO 2 emissions by its conversion into methanol at mild conditions, however, its performance depends on the optimization of the alloy-support effects, which is unclear up to now. Herein, we investigate the influence of alloy-support synergy in the catalytic performance of Ni 5 Ga 3 supported on SiO 2 , CeO 2, and ZrO 2 , by combining in-depth structural, chemical and spectroscopic characterization and density functional theory (DFT) calculations. In situ DRIFTS confirmed further hydrogenation of key reaction intermediates in Ni 5 Ga 3 /ZrO 2 surface, while weak CO 2 adsorption in Ni 5 Ga 3 /SiO 2 avoided intermediate stabilization on the surface and, strong interaction with Ni 5 Ga 3 /CeO 2 poisoned interface active sites. Additionally, the relative energies of reactants and key intermediates in the three distinct regions of the catalyst (support surface, alloy surface, and alloy-support interface), calculated through DFT, allowed us to propose a reaction mechanism for the most promising catalyst, Ni 5 Ga 3 /ZrO 2. [Display omitted] • Support effects on the performance of Ni 5 Ga 3 catalysts were evaluated during CO 2 hydrogenation to methanol. • Weak CO 2 adsorption in Ni 5 Ga 3 /SiO 2 limited the methanol production through an alloy surface mechanism. • The strong interaction of CO 2 and reaction intermediates in the Ni 5 Ga 3 /CeO 2 interface poisoned the active sites. • Ni 5 Ga 3 /ZrO 2 interface was capable of stabilizing key reaction intermediates and promote further hydrogenation to methanol. • Combined in situ spectroscopy analysis and DFT calculations allowed to propose a reaction mechanism for Ni 5 Ga 3 /ZrO 2 system. [ABSTRACT FROM AUTHOR]

An atomistic understanding of the interaction between Au clusters and dichalcogenides nanoflakes of different polytypes is fundamental to improve our knowledge to the tuning of the physical-chemical properties of hybrid dimensional composite materials. Here, we report a density functional theory investigation into the changes of structural, energetic, and electronic properties induced by the adsorption of Au 4 clusters (planar and tetrahedron) onto Mo 16 Se 32 and Mo 3 6Se 7 2 nanoflakes of both 1T' and 2H polytypes. We found that the Au–Se interaction plays a critical role in the nature of the Au 4 /MoSe 2 interactions, in which there is a strong energetic preference for the S atoms located at the edges for all nanoflake sizes and polytypes. In summary, the Au⋯MoSe 2 binding mechanisms is composed of either (i) splitting of Se sp 2-orbitals interacting with Au sd 3-orbitals, or (ii) re-hybridized Au sd 3 splitting of Mo d z 2 -orbitals, with low charge transfer in both due to Au 4 cluster electron filling. Furthermore, the cluster/nanoflake adsorption energetics and structural distortions due to the Au⋯MoSe 2 interactions are mainly determined by the MoSe 2 edge configurations. Image 1 • We found that laterally stacked Au4/1T0-MoSe2 are the most stable configurations for both nanoflakes sizes, but with laterally stacked Au4/2H–MoSe2 exhibiting the more intense adsorption energies due to interaction of the Au4 clusters with 2H–MoSe2 armchair and zigzag configurations. • The S atoms at the edges plays a critical role in the Au-MoSe2 interactions. • The adsorption properties of Au4 on the MoSe2 nanoflakes are mainly determined by the edge configurations. [ABSTRACT FROM AUTHOR]