Evolution of the atomic and electronic structures of CuO clusters: a comprehensive study using the DFT approach.

One of the most fundamental aspects of cluster science is to understand the structural evolution at the atomic scale. In this connection, here we report a comprehensive study of the atomic and electronic structures of (CuO)n clusters for n = 1 to 12 using DFT-based formalisms. Both the plane wave-based pseudo-potential approach and LCAO-MO-based method have been employed to obtain the ground state geometries of neutral, cation and anion copper oxide clusters. The results reveal that neutral copper oxide clusters favor a planar ring structure up to heptamer and from octamer onwards they adopt a three-dimensional motif with (CuO)9 and (CuO)12 forming a barrel-shaped layered structure. Detailed electronic structure analysis reveals that the transition of the atomic structure from 2D to 3D is guided by the energy balance of the Cu-O (d-p) and Cu-Cu (d-d) bonds. The removal of one electron from the cluster (cation) results in slightly stretched bonds while the addition of one electron (anion) showed compression in the overall geometries. The thermodynamic and electronic stability of these clusters has been analyzed by estimating their binding energy, ionization energy and electron affinity as a function of size. Remarkably, among these clusters, the octamer (CuO)8 and dodecamer (CuO)12 show higher binding energy and electron affinity (∼6.5 eV) with lower ionization energy (5.5-6.0 eV). This unique feature of the octamer and dodecamer indicates that they are very promising candidates for both oxidizing and reducing agents in different important chemical reactions.

Probing Kinetics and Mechanism of Formation of Mixed Metallic Nanoparticles in a Polymer Membrane by Galvanic Replacement between Two Immiscible Metals: Case Study of Nickel/Silver Nanoparticle Synthesis.

Galvanic replacement between metals has received notable research interest for the synthesis of heterometallic nanostructures. The growth pattern of the nanostructures depends on several factors such as extent of lattice mismatch, adhesive interaction between the metals, cohesive forces of the individual metals, etc. Due to the difficulties in probing ultrafast kinetics of the galvanic replacement reaction and particle growth in solution, real-time mechanistic investigations are often limited. As a result, the growth mechanism of one metal on the surface of another metal at the nanoscale is poorly understood so far. In the present work, we could successfully probe the galvanic replacement of silver ions with nickel nanoparticles, stabilized in a polymer membrane, using two complementary methods, namely, small-angle X-ray scattering (SAXS) and radiolabeling, and the results are supported by density functional theory (DFT) computations. The silver-nickel system has been chosen for the present investigation because of the high degree of bulk immiscibility caused by the large lattice mismatch (15.9%) and the weak adhesive interaction, which makes it a perfect model system for immiscible metal pairs. Membrane, as a host medium, plays a crucial role in retarding the kinetics of atomic and particle rearrangements (nucleation and growth) due to slower mobility of the atoms (monomers) and particles within the polymer network. This allowed us to examine the real-time concentration of silver monomers during galvanic replacement of silver ions with nickel nanoparticles and evolution of Ni/Ag nanoparticles. From combined experiment and DFT computations, it has been demonstrated, for the first time to the best of our knowledge, that the majority of silver atoms, which are produced on the nickel nanoparticle surface by galvanic reactions, do not form traditional core-shell nanostructures with nickel and undergo a self-governing sequential nucleation and growth of silver nanoparticles via formation of intermediate prenucleation silver clusters, leading to the formation of mixed metallic nanoparticles in the membrane. The surface of NiNPs has a heterogeneous effect on the silver nucleation pathway, which is evident from the reduced critical free energy barrier of nucleation (ΔGcrit). The present work establishes an original mechanistic pathway based on a sequential nucleation model for formation of mixed metallic nanoparticles by the galvanic replacement route, which opens up future possibilities for size-controlled synthesis in mixed systems.

Half metallicity and ferromagnetism of vanadium nitride nanoribbons: a first-principles study.

Half metallic materials with intrinsic ferromagnetism are identified as the pillar of next generation spintronic devices. In search of new low-dimensional materials with these excellent properties, herein we systematically study the electronic and magnetic properties of edge dependent (armchair (ac) and zigzag (zz)) vanadium nitride nanoribbons (VNNRs) using density functional theory (DFT) based calculations. Both the ac and zz VNNRs show robust ferromagnetism and extensive half-metallicity with large band gaps (3.9-4.3 eV for ac and 2.5-3.0 eV for zz VNNRs) for the down spin channel. Interestingly, even with the application of uniaxial strain (both tensile and compressive) along the axis of the ribbons, VNNRs retain their extensive half metallicity with a large spin band gap and robust ferromagnetic behavior. Spin dependent electronic transport reveals the 100% spin filtering efficiency of nanoribbons, in both the free state and under applied strain, which support the robust half metallicity of VNNRs. Our study of VNNRs on a MoS2 substrate also shows half metallicity along with high stability, indicating the usage of MoS2 as a substrate for the synthesis of VNNRs. All these results guide the potential application of VNNRs in spintronic devices.

Tuning of electron tunneling: a case study using BODIPY molecular layers.

Redox active π-conjugated organic molecules have shown the potential to be used as electronic components such as diode and memory elements. Here, we demonstrate that using simple surface chemistry, rectification characteristics can be tuned to reproducible negative differential resistance (NDR) with a very high peak-to-valley ratio (PVR) up to 1000 in 2,6-diethyl-4,4-difluoro-1,3,5,7,8-pentamethyl-4-bora-3a,4a-diaza-s-indecene (BODIPY) grafted on Si. The change in properties is related to oxidation and reduction of BODIPY, which results in the change in resonant to non-resonant tunneling of electrons under bias. This has been explained by the ab initio molecular-orbital theoretical calculations.

Bimetallic Ag-Pt Sub-nanometer Supported Clusters as Highly Efficient and Robust Oxidation Catalysts.

A combined experimental and theoretical investigation of Ag-Pt sub-nanometer clusters as heterogeneous catalysts in the CO→CO2 reaction (COox) is presented. Ag9 Pt2 and Ag9 Pt3 clusters are size-selected in the gas phase, deposited on an ultrathin amorphous alumina support, and tested as catalysts experimentally under realistic conditions and by first-principles simulations at realistic coverage. In situ GISAXS/TPRx demonstrates that the clusters do not sinter or deactivate even after prolonged exposure to reactants at high temperature, and present comparable, extremely high COox catalytic efficiency. Such high activity and stability are ascribed to a synergic role of Ag and Pt in ultranano-aggregates, in which Pt anchors the clusters to the support and binds and activates two CO molecules, while Ag binds and activates O2 , and Ag/Pt surface proximity disfavors poisoning by CO or oxidized species.

ORR viability of alumina-supported platinum nanocluster: exploring oxidation behaviour by DFT.

While alumina-supported platinum particles are versatile for several oxidation reactions, their viability as ORR catalysts has not been explored to date. Therefore, to assess the prospects of alumina-supported platinum nanoclusters in ORRs, a systematic DFT study has been carried out to explore the oxidation behavior of a Ptn@Al2O3 (n = 1-7, 10) cluster. The results are compared with the oxidation behavior of the corresponding gas phase platinum cluster and that of an extended Pt(111) slab. Both supported and unsupported clusters activate adsorbed oxygen molecules and energetically favor dissociative chemisorption of oxygen, leading to stable oxide formation with Pt-O-Pt linkages. However, the influence of the alumina substrate downshifts the d-band centre of the platinum cluster, which not only reduces the reaction enthalpy of oxidation by 8-10%, but also elongates the Pt-O bond of the oxide product by 3-8%. These observations indicate that removal of oxide will be relatively easier for supported clusters than for unsupported clusters. Cluster binding is found to sustain during oxidation, as oxidation of the platinum host cluster results in reduction of the distance between the cluster and support surface. While the gas phase Pt10 cluster does not show any similarity to the oxidation behavior shown by THE Pt(111) slab, the Pt10@Al2O3 cluster reveals close resemblance. Both the Pt(111) slab and Pt10@Al2O3 cluster form similar oxide products, having tri-coordinated oxygen with comparable Pt-O bond distances. The observed resemblance has been attributed to the similarity in the electronic structure and d-band centre position of the platinum surface and alumina-supported Pt10 cluster. Whilst this similar oxidation behaviour of the Pt10@Al2O3 cluster endorses its viability as an ORR catalyst, further modulation of this catalyst is desirable to improve its potential.

Platinum-Mediated Activation of Coordinated Organonitriles by Telluroethers in Tetrahydrofuran: Isolation, Structural Characterization, and Density Functional Theory Analysis of Intermediate Complexes.

The reactions of [PtCl2(NCR)2] with telluroethers (ArAr'Te) in organic solvents have been investigated. The reactions in dichloromethane yield [PtCl2(TeArAr')2], while those in tetrahydrofuran (THF) give different products depending on the steric demands of the aryl groups on tellurium, the molarity of the reactants, and the reaction conditions. The reactions between [PtCl2(PhCN)2] and TeArAr' in 1:1 molar ratio at room temperature in THF yield several products, like [PtCl2(TeArAr')2] (Ar/Ar' = Ph/Ph, o-tol/Mes, Mes/Mes), [PtCl2(PhCN){NC(O)Ph[TeMes(o-tol)]}], and [PtCl2{NC(O)Ph(TeMes2)}2]. The reaction with TeMes2 in refluxing THF gave [PtCl2{NC(Ph)C4H7O}{NC(O)Ph(TeMes2)}] and [PtCl(TeMes2){Te(Mes)CH2C6H2Me2}], depending on the duration of heating. Reaction of [PtCl2(PhCN)2] with TeArMes afforded [PtCl2(TeArMes)2] (Ar = Ph, o-tol, and Mes), the formation of which decreased with increasing steric demand of the Ar group, together with [PtCl2{NC(O)Ph(TeArMes)}2]. The telluroether in the latter binds to nitrogen, and tellurium exists in the formal oxidation state of +4 (from XPS). The tellurium in these complexes exhibits secondary interactions with platinum (J((195)Pt-(125)Te) = 309-347 Hz) and with the carbonyl oxygen. These complexes slowly dissociate in solution to give [PtCl2(TeMesAr){NC(O)Ph(TeMesAr)}], finally leading to the formation of [PtCl2(TeMesAr)2]. Molecular structures of trans-[PtCl2(PhCN){NC(O)Ph[TeMes(o-tol)]}], trans-[PtCl2{NC(O)Ph(TeMes2)}2], trans-[PtCl2{NC(Ph)C4H7O}{NC(O)Ph(TeMes2)}], trans-[PtCl2{NC(O)Ph[TeMes(o-tol)]}2], trans-[PtCl2(TeMes2){NC(O)Ph(TeMes2)}], trans-[PtCl2{NC(O)Me(TeMes2)}2], and [PtCl(Te-o-tol){NC(O)Ph}2] have been unambiguously established by single-crystal X-ray diffraction analyses. Density functional theory calculations for some of the complexes were performed, and geometrical parameters are in good agreement with the values obtained from X-ray analyses.

Evidence of a graphene-like Sn-sheet on a Au(111) substrate: electronic structure and transport properties from first principles calculations.

Two dimensional nanostructures of group IV elements have attracted a great deal of attention because of their fundamental and technological applications. A graphene-like single layer of tin atoms, commonly called stanene, has recently been predicted to behave like a quantum spin Hall insulator. Here we report the atomic structure, stability and electron transport properties of stanene stabilized on a gold substrate. The optimization of geometry and electronic structure was carried out using a plane-wave based pseudo-potential approach. This work is divided into three parts: (i) the nature of chemical interaction between tin atoms and the gold support, (ii) the geometrical shape and electronic structure of the tin layer on the gold support and (iii) the electron transport behavior of the gold supported tin layer. The results show that tin atoms bind to the gold support through strong chemical bonds and significant electronic charge transfer occurs from tin to the gold support. Remarkably, for a layer of tin atoms, while a buckled structure is preferred in the free state, a planar graphene-like atomic arrangement is stabilized on the gold support. This structural change corroborates the metal-like band structure of the planar stanene in comparison to the semi-metallic buckled configuration. The tunneling current of the supported tin layer shows Ohmic-like behavior and the calculated STM pattern of the supported tin layer shows distinct images of 'holes', characteristic of the hexagonal lattice.

Silicon-pyrene/perylene hybrids as molecular rectifiers.

We have synthesized two alkenyl (C-6 and C-11 chains) pyrenes and one alkenyl (C-11 chain) perylene as the σ-π systems, which were electro-grafted on H-terminated Si surfaces to form the respective monolayers. The I-V characteristics of the monolayers revealed pronounced rectification in forward bias with a maximum rectification ratio (RR) of 2.5 × 10(5) at 2.5 V for the C-6-pyrene 4b, 1000 at 1.5 V for the C-11-pyrene 4a and 3000-5000 at 1.75 V for the C-11-perylene 3. The higher RR of the devices containing 4b compared to those of 4a and 3 is possibly due to better alignment and packing of the 4b-monolayers on the Si substrate. The rectification was explained using the ab initio molecular-orbital calculations.

The structural and electronic properties of Au(n) clusters on the α-Al2O3(0001) surface: a first principles study.

We report the structural and electronic properties of Aun (n = 1-7 and 10) clusters supported on a clean α-Al2O3(0001) surface using the spin-polarized version of the plane wave based pseudo-potential method. To underscore the effect of support interaction, the geometries of the deposited Au clusters are compared with the gas-phase structures. In general, the trend in the growth pattern shows that all deposited Au clusters favor planar configurations, similar to that in the isolated case. However, due to the roughness of the Al2O3(0001) surface the deposited Au atoms are arranged in a zig-zag pattern. The binding energy of an Au atom on the Al2O3 surface is 0.79 eV and it binds to the surface Al atom. Two Au atoms prefer to form a dimer on the alumina surface rather than adsorbing as a monomer at a long distance. As the size of the cluster increases the adsorption energy shows a decreasing trend. The nature of chemical bonding at the interface is established by the charge distribution analysis, which suggests an overall charge transfer from the surface to the Au cluster. The additional negative charge on the deposited Au cluster corroborates the red shift of the energy levels of the Au-Al2O3 composite in comparison to the isolated Aun clusters. Further investigations were carried out by analyzing the interaction between the oxygen molecule and the Aun@Al2O3 system, a prototype to study the oxidation mechanism. The results reveal that the interaction of O2 with Aun@Al2O3 follows a dissociative chemisorption route and ruptures the O-O bond.

Do Ag(n) (up to n = 8) clusters retain their identity on graphite? Insights from first-principles calculations including dispersion interactions.

Adsorption of pre-formed Agn clusters for n = 1 - 8 on a graphite substrate is studied within the density functional theory employing the vdW-DF2 functional to treat dispersion interactions. Top sites above surface layer carbon atoms turn out to be most favorable for a Ag adatom, in agreement with experimental observations. The same feature is observed for clusters of almost all sizes which have the lowest energies when the Ag atoms are positioned over top sites. Most gas phase isomers retain their structures over the substrate, though a couple of them undergo significant distortions. Energetics of the adsorption can be understood in terms of a competition between energy cost of disturbing Ag-Ag bonds in the cluster and energy gain from Ag-C interactions at the surface. Ag3 turns out to be an exceptional candidate in this regard that undergoes significant structural distortion and has only two of the Ag atoms close to surface C atoms in its lowest energy structure.

Sustainability of the effect of optical intervention on the reading performance of children with dyslexia.

Background: Dyslexia is a learning disability associated with reading difficulties in children. Due to the potential of poor school outcomes interventions have been employed to help students with dyslexia read. This study was aimed at identifying the sustainability of the effect of combined Visual Tracking Magnifier (VTM) and Ministry of Education (MOE) interventions and MOE intervention alone on the reading performance of school children with dyslexia after discontinuation of intervention. Methods: This prospective, interventional study was conducted on primary school children with dyslexia aged 8 - 11 years. The participants underwent comprehensive ophthalmic and optometric examinations and were categorized into groups A, B, and C, comprising primary school children at level 1 or 2. Groups A and B received combined VTM and MOE interventions for 12 and 24 weeks, respectively, and group C received MOE intervention alone. The reading performance was assessed at baseline and 12, 24, and 36 weeks post-intervention. Results: Both components of the reading performance improved significantly for school children at both levels in all study groups (all P < 0.05). However, the reading performance improvement was only approximately 28% in group C and 38% - 50% in groups A and B. In group A, students at level 1 showed significantly improved reading speed from baseline to 12 weeks post-VTM intervention and reading rate from baseline to 24 weeks post-VTM intervention (both P < 0.05). Students at level 2 showed significantly improved reading speed and rate from baseline to 12 and 24 weeks post-VTM intervention (all P < 0.05). In group B, students at both levels showed significantly improved reading speed and rate from baseline to 24 and 36 weeks post-VTM intervention (all P < 0.05). Students at level 2 showed significantly improved reading speed 12 weeks after cessation of intervention (at 36 weeks post-VTM intervention) compared to 24 weeks post-VTM intervention (P < 0.05). The improvement remaining stable 12 weeks after discontinuation of intervention indicated a sustained effect. Conclusions: Combined or individual intervention improved the reading performance of school children with dyslexia at levels 1 and 2. However, combined intervention showed a better reading improvement effect. Improvement in the reading performance was maintained after discontinuation of the VTM intervention. Further interventional studies with a longer study period after discontinuation of this optical intervention are required to confirm the long-term sustainability of its positive effects on the reading performance of school children with dyslexia.

Distribution of refractive error among chinese primary school children in a rural area in Pahang, Malaysia.

Purpose: This study aimed to determine the prevalence and status of refractive error among Chinese primary school children in a rural area in Pahang. Methods: This investigation entailed a cross-sectional retrospective study design involving case file analyses. The study site was a Chinese medium primary school in a rural locality within Bentong district. A total of 82 school children met the B40 classification and selection criteria; therefore, universal sampling was done. Analyses were done according to age group: Level 1 included ages 7 to 9 years, while Level 2 comprised 10- to 12-year-olds. Results: The mean age of the 82 Chinese school children was 9.72±1.5 years; the percentage of refractive errors found was 80.48%. A total of 53 (64.63%) children had myopia. Two-way ANOVA showed a significant difference (P=0.038) in the refractive error between age groups Level 1 and 2, but no significant difference (P=0.947) was observed in refractive error between genders. The chi-square test and Fishers exact test showed no significant association between the type of refractive error with gender (P>0.05) and age group (P=0.319). Conclusion: Myopia was the most common type of refractive error among Chinese school children in a rural area in Pahang. Refractive error severity was influenced by age group but not by gender. Types of refractive error were not associated with age group and gender. Hence, it is recommended that Chinese school children in rural areas seek an annual vision screening or eye test.

Characteristics of eye injuries, medical cost and return-to-work status among industrial workers: a retrospective study.

OBJECTIVE: The aim of this study is to determine the characteristics of eye injuries, medical costs and return-to-work status among industrial workers to provide better vision rehabilitative services. SETTING: Nationwide data from the Social Security Organisation (SOCSO) of Malaysia. PARTICIPANTS: A stratified random sample of workers registered with the SOCSO of Malaysia with documentation of eye injury. PRIMARY AND SECONDARY OUTCOME MEASURES: Characteristics of eye injuries and medical costs related to eye injury (primary) and return-to-work status (secondary). RESULTS: A total of 884 from 8861 case files workplace accidents involving eye injury registered with Social Security Services (SOCSO) were identified. The mean age was 35±10 years and the highest incidence of work-related eye injury occurred in the age group 30-39 years and among Malay ethnics. Males are affected more than females' workers. The highest cause of eye injury was the impact from a moving object excluding falling objects (89.2%) and anterior segment injuries occurred more than posterior segment injuries. The total direct and Indirect medical cost was RM1 108 098.00 (US$316 599.40) and RM4 150 140.00 (US$1 185 754.20) for 884 cases. CONCLUSION: The majority of workers suffered from the low level of eye injury. A significant relationship was found between the severity of eye injury and employee work status. The indirect cost of medical and vision rehabilitation was higher than the direct cost. Awareness and vision rehabilitation programmes at the workplace need to be addressed for better prevention and rehabilitative service.

Growth pattern of Ag(n) (n = 1-8) clusters on the α-Al2O3(0001) surface: a first principles study.

We report an extensive first-principles study of the structure and electronic properties of Ag(n) (n = 1-8) clusters isolated in gas phase and deposited on the α-Al(2)O(3) surface. We have used the plane wave based pseudopotential method within the framework of density functional theory. The electron ion interaction has been described using projector augmented wave (PAW), and the spin-polarized GGA scheme was used for the exchange correlation energy. The results reveal that, albeit interacting with support alumina, the Ag atoms prefers to remain bonded together suggesting an island growth motif is preferred over wetting the surface. When compared the equilibrium structures of Ag clusters between free and on alumina substrate, a significant difference was observed starting from n = 7 onward. While Ag(7) forms a three-dimensional (3D) pentagonal bipyramid in the isolated gas phase, on alumina support it forms a planar hexagonal structure parallel to the surface plane. Moreover, the spin moment of the Ag(7) cluster was found to be fully quenched. This has been attributed to higher delocalization of electron density as the size of the cluster increases. Furthermore, a comparison of chemical bonding analysis through electronic density of state (EDOS) shows that the EDOS of the deposited Ag(n) cluster is significantly broader, which has been ascribed to the enhanced spd hybridization. On the basis of the energetics, it is found that the adsorption energy of Ag clusters on the α-Al(2)O(3) surface decreases with cluster size.

Amplitude of Accommodation among Students of a Malaysian Private University as Assessed Using Subjective and Objective Techniques.

PURPOSE: The purpose of the study was to establish baseline data for amplitude of accommodation (AA) measured using both subjective and objective techniques in students at a private Malaysian university. METHODS: This cross-sectional study was conducted including 34 healthy participants with a mean age of 22.26 ± 1.88 years. AA was measured using dynamic retinoscopy and the push-up, pull-away, modified push-up, and minus-lens techniques. RESULTS: The mean AA scores for the push-up, pull-away, minus-lens, and modified push-up techniques and dynamic retinoscopy were 11.38 ± 2.03, 10.35 ± 1.64, 9.24 ± 1.18, 8.26 ± 1.44, and 7.2 ± 1.0 diopters, respectively. No AA measurements showed significant difference among ethnicities (Chinese, Malay, and Indian). This study suggested that AA obtained using push-up (p = 0.005) and pull-away (p = 0.017) methods and dynamic retinoscopy (p = 0.041) were significantly different according to sex. No significant difference was observed in AA for the minus-lens (p = 0.051) and modified push-up (p = 0.216) techniques by sex. A moderately negative correlation was found between AA and age for the push-up (r = -0.434, p = 0.010), pull-away (r = -0.412, p = 0.016), and minus-lens (r = -0.509, p = 0.002) techniques and dynamic retinoscopy (r = -0.497, p = 0.003). A weak negative correlation was found between age and AA measured using a modified push-up technique (r = -0.393, p = 0.022). CONCLUSIONS: Mean AA was highest for the push-up technique, followed by the pull-away technique, the minus-lens technique, the modified push up technique, and dynamic retinoscopy. The push-up and pull-away methods and dynamic retinoscopy showed a significant difference in measurement of AA between sexes.

Oxidation of Al doped Au clusters: a first principles study.

Using first principles method we report the oxidation of Al doped Au clusters. This work is divided into two parts: (i) the equilibrium structures and stability of Al doped Au(n-1) clusters (n=2-7,21) and (ii) the interaction of O(2) with stable clusters. The calculations are performed using the plane wave pseudopotential approach under the density functional theory and generalized gradient approximation for the exchange and correlation functional. The optimized geometries of Au(n-1)Al clusters indicate that the substitution of Au by Al results an early onset of three-dimensional structures from tetramer onwards. This is different from the results of transition metal doped Au clusters, where the planar conformation of Au clusters retains up to heptamer. The stability of Au(n-1)Al clusters has been analyzed based on the binding energy, second difference in energy, and the energy gaps between the highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels. Based on the energetics, the Au(3)Al and Au(5)Al clusters are found to have extraordinary stability. The oxidation mechanism of Al doped Au clusters have been studied by the interaction of O(2) with Al, Au, AuAl, Au(3)Al, and Au(20)Al clusters. It is found that the oxidation of Au(n-1)Al clusters undergoes via dissociative mechanism, albeit significant charge transfer from Al to Au. Moreover, the O(2) molecule prefers to attach at the Al site rather than at the Au site.

A theoretical study on the interaction of aromatic amino acids with graphene and single walled carbon nanotube.

In this study we have investigated the interaction of phenylalanine (Phe), histidine (His), tyrosine (Tyr), and tryptophan (Tryp) molecules with graphene and single walled carbon nanotubes (CNTs) with an aim to understand the effect of curvature on the non-covalent interaction. The calculations are performed using density functional theory and the Moller-Plesset second-order perturbation theory (MP2) within linear combination of atomic orbitals-molecular orbital (LCAO-MO) approach. Using these methods, the equilibrium configurations of these complexes were found to be very similar, i.e., the aromatic rings of the amino acids prefer to orient in parallel with respect to the plane of the substrates, which bears the signature of weak pi-pi interactions. The binding strength follows the trend: His

Growth pattern and electronic properties of acetonitrile clusters: a density functional study.

We report a systematic theoretical study on the growth pattern and electronic properties of acetonitrile clusters [(CH(3)CN)(n) (n = 1, 9, 12)] using density functional approach at the B3LYP6-31++G(d,p) level. Although we have considered a large number of configurations for each cluster, the stability of the lowest energy isomer was verified from the Hessian calculation. It is found that the lowest energy isomer of the dimer adopts an antiparallel configuration. For trimer and tetramer, cyclic ring structures were found to be favored over the dipole stabilized structure. In general, it is found that the intermolecular CH...N interactions play a significant role in the stabilization of the cyclic layered geometry of acetonitrile clusters. A critical comparison between trimer and tetramer clusters suggests that the three member cyclic ring is more stable than four member rings. The growth motif for larger clusters (n = 5-9, 12) follows a layered pattern consisting of three or four membered rings, which, in fact, is used as the building block. Based on the stability analysis, it is found that clusters with an even number of molecular entities are more stable than the odd clusters, except trimer and nonamer. The exceptional stability of these two clusters is attributed to the formation of trimembered cyclic rings, which have been found to form the building blocks for larger clusters.

Single atom alloy catalyst for SO3 decomposition: enhancement of platinum catalyst's performance by Ag atom embedding.

Recently, single atom alloy catalysts (SAA) have shown improved catalytic activity in numerous catalytic reactions. However, to date, single atom alloy (SAA) catalyst is not available for SO3 decomposition reaction, which is a key reactions in the hydrogen economy. Using state of the art density functional theory, we report a novel single Ag atom alloy Pt catalyst in the sub-nanometer length scale (AgPt9@Al2O3) showing superior catalytic behavior for SO3 decomposition. It was found that alloying the alumina-supported platinum nanocluster with a single Ag atom lowers the activation barrier for S-O bond breaking by more than 50% in comparison with the pristine platinum counterpart. Activation barrier for AgPt9@Al2O3 catalyst is 0.52 eV, which is the lowest of any platinum based catalyst reported so far. At variance with pure Pt10@Al2O3, which tries to detach from the support during decomposition reaction, single atom alloy (SAA) nanocluster AgPt9@Al2O3 enhances binding with support, thus strengthening sintering resistance. Notably, influence of single Ag atom is also observed at larger length scale, i.e., at Pt(111) slab, where single Ag atom substituted surface Ag1Pt(111) shows ∼30% reduction in activation barrier in contrast to a pristine surface. Single Ag atom works in bifunctional mode as it not only reduces the activation barrier, but also simultaneously weakly adsorbs the reaction product SO2, signifying relatively easier desorption and better recyclability. Deeper location of silver d-electrons and lesser electronegativity of silver is responsible for the better performance of single Ag atom alloyed Pt catalyst. We strongly believe that these remarkable results will open new avenues for future designing and fabrication of cost-effective catalysts for SO3 decomposition.