Interaction Of N2 Research Articles

Innovative proposal for N2 capturing in Liquid Argon using the Li-FAU molecular Sieve

In this work, we unveil the potential of nitrogen (N2) adsorption from Liquid Argon (LAr) through the molecular sieves (zeolites) Li-FAU Adsorbents. We report detailed studies about N2 gas adsorption at T = 89 K using a commercial Micromeritics ASAP-2420 equipment and N2 purification from LAr using the Purification Cryostat (PuLArC) at IFGW/Unicamp. We argue that the N2 adsorption by the Li-FAU is possible thanks to the stronger interaction of N2 with the lithium cations present in zeolite Li-FAU. In fact, the experiments performed in PuLArC have unequivocally shown that the Li-FAU adsorbent was capable of capturing N2, reducing a N2 contamination of 20–50 ppm to 0.1–1.0 ppm in 1–2 hours of circulation time in LAr for several runs.This result demonstrated the great potential of the Li-FAU adsorbent for N2 capturing in LAr and invoke further tests of this material in larger scale LAr cryostats in order to confirm the innovative proposal of using the Li-FAU molecular sieve in replacement of Molecular Sieve 4A, currently used in LAr cryostats for neutrino experiments.

Engineered Electron-Deficient Sites at Boron-Doped Strontium Titanate/Electrolyte Interfaces Accelerate the Electrocatalytic Reduction of N2 to NH3: A Combined DFT and Experimental Electrocatalysis Study.

The development of an efficient, selective, and durable catalysis system for the electrocatalytic N2 reduction reaction (ENRR) is a promising strategy for the sustainable production of ammonia. The high-performance ENRR is limited by two major challenges: poor adsorption of N2 over the catalyst surface and abysmal N2 solubility in aqueous electrolytes. Herein, with the help of our combined density functional theory (DFT) calculations and experimental electrocatalysis study, we demonstrate that concurrently induced electron-deficient Lewis acid sites in an electrocatalyst and in an electrolyte medium can significantly boost the ENRR performance. The DFT calculations, ex situ X-ray photoelectron and FTIR spectroscopy, electrochemical measurements, and N2-TPD (temperature-programmed desorption) over boron-doped strontium titanate (BSTO) samples reveal that the Lewis acid-base interactions of N2 synergistically enhance the adsorption and activation of N2. Besides, the B-dopant induces the defect sites (oxygen vacancies and Ti3+) that assist in enhanced N2 adsorption and results in suppressed hydrogen evolution due to B-induced electron-deficient sites for H+ adsorption. The insights from the DFT study evince that B prefers the Srtop position (on top of Sr) where N2 adsorbs in an end-on configuration, which favors the associative alternating pathway and suppresses the competitive hydrogen evolution. Thus, our combined experimental and DFT study demonstrates an insight toward enhancing the ENRR performance along with the suppressed hydrogen evolution via concurrently engineered electron-deficient sites at electrode and electrolyte interfaces.

DFT insights into the electronic properties and gas sensing performance of C19X (X = C, N, and Si) nanocages for the detection of CO2, CO, N2, and H2 gases

The development of carbon nanocage-based sensors for the detection of toxic and pollutant gases has attracted significant attention from researchers. In this computational study, the interactions of CO2, CO, N2, and H2 gases with the C19X nanocages (X = C, N, and Si) were evaluated using the M062X/6-31G(d) level of density functional theory (DFT) calculations. The results demonstrated a reduction in the energy gap (Egap) across all studied systems, especially pronounced in the C19N and C19Si nanocages, compared to the complexes with a higher priority of the C19Si nanocages. The gas molecules were found to have weak adsorption in all the C20 nanocage complexes, while the adsorption of CO gas was more pronounced in the C19N and C19Si nanocages compared to the other gases studied. A quantum theory of atoms in molecule (QTAIM) analysis was conducted to examine the interactions and their features, through which the physical interactions that contribute to the formation of the complexes were identified. Further electrical characterizations revealed that the C19Si nanocage has a high sensitivity for the detection of CO gas, making it a promising sensor material. In conclusion, the engineered C19N and C19Si nanocages demonstrated significant improvements over the original C20 nanocage in terms of adsorption capabilities for CO2, CO, N2, and H2 gases, making them promising candidates for sensor applications.

Interaction of N2, O2 and H2 Molecules with Superalkalis.

Superalkalis (SAs) are exotic clusters having lower ionization energy than alkali atoms, which makes them strong reducing agents. In the quest for the reduction of diatomic molecules (X2) such as N2, O2, and H2 using Møller-Plesset perturbation theory (MP2), we have studied their interaction with typical superalkalis such as FLi2, OLi3, and NLi4 and calculated various parameters of the resulting SA-X2 complexes. We noticed that the SA-O2 complex and its isomers possess strong ionic interaction, which leads to the reduction of O2 to O2 - anion. On the contrary, there are both ionic and covalent interactions in SA-N2 complexes such that the lowest energy isomers are covalently bonded with no charge transfer from SA. Further, the interaction between SA and H2 leads to weakly bound complexes, which results in the adsorption of H2 molecules. The nature of interaction is found to be closely related to the electron affinity of diatomic molecules. These findings might be useful in the study of the activation, reduction, and adsorption of small molecules, which can be further explored for their possible applications.

Atomic insights into the interaction of N2, CO2, NH3, NO, and NO2 gas molecules with Zn2(V, Nb, Ta)N3 ternary nitride monolayers.

The search for promising carrier blocking layer materials with high stability, including resistance to surface inhibition by environmental molecules that cause a drop in carrier mobility, is critical for the production of tandem solar cells. Based on density functional theory calculations, the reaction of atmospheric gases, including N2, CO2, NH3, NO, and NO2, with three promising Zn2(V, Nb, Ta)N3 monolayers is discovered. The results suggest the chemical adsorption of NH3 and physical adsorption of NO and NO2. In addition, the Zn2(V, Nb, Ta)N3 monolayers are characterized by a weak bonding with N2 and CO2. Charge redistribution is found at the interface between the monolayers and NH3, NO and NO2 molecules, leading to the formation of a local surface dipole that affects the functionality of the Zn2(V, Nb, Ta)N3 monolayers. The Zn2VN3 monolayer is less reactive with atmospheric gases and thus is the most promising for application in tandem solar cells. Notably, the revealed nontrivial behavior of the Zn2(V, Nb, Ta)N3 monolayers towards N-containing gases makes them promising for application in gas sensing. Specifically, the Zn2TaN3 monolayer is the most promising for application in molecular sensing due to its high reversibility and distinguished interaction with NH3, NO, and NO2 gases.

Iron promoted end-on dinitrogen-bridging in heterobimetallic complexes of uranium and lanthanides.

End-on binding of dinitrogen to low valent metal centres is common in transition metal chemistry but remains extremely rare in f-elements chemistry. In particular, heterobimetallic end-on N2 bridged complexes of lanthanides are unprecedented despite their potential relevance in catalytic reduction of dinitrogen. Here we report the synthesis and characterization of a series of N2 bridged heterobimetallic complexes of U(iii), Ln(iii) and Ln(ii) which were prepared by reacting the Fe dinitrogen complex [Fe(depe)2(N2)] (depe = 1,2-bis(diethylphosphino)-ethane), complex A with [MIII{N(SiMe3)2}3] (M = U, Ce, Sm, Dy, Tm) and [LnII{N(SiMe3)2}2], (Ln = Sm, Yb). Despite the lack of reactivity of the U(iii), Ln(iii) and Ln(ii) amide complexes with dinitrogen, the end-on dinitrogen bridged heterobimetallic complexes [{Fe(depe)2}(μ-η1:η1-N2)(M{N(SiMe3)2}3)], 1-M (M = U(iii), Ce(iii), Sm(iii), Dy(iii) and Tm(iii)), [{Fe(depe)2}(μ-η1:η1-N2)(Ln{N(SiMe3)2}2)], 1*-Ln (Ln = Sm(ii), Yb(ii)) and [{Fe(depe)2(μ-η1:η1-N2)}2{SmII{N(SiMe3)2}2}], 3 could be prepared. The synthetic method used here allowed to isolate unprecedented end-on bridging N2 complexes of divalent lanthanides which provide relevant structural models for the species involved in the catalytic reduction of dinitrogen by Fe/Sm(ii) systems. Computational studies showed an essentially electrostatic interaction of the end-on bridging N2 with both Ln(iii) and Ln(ii) complexes with the degree of N2 activation correlating with their Lewis acidity. In contrast, a back-bonding covalent contribution to the U(iii)-N2Fe bond was identified by computational studies. Computational studies also suggest that end-on binding of N2 to U(iii) and Ln(ii) complexes is favoured for the iron-bound N2 compared to free N2 due to the higher N2 polarization.

Quantum Chemical Simulations of CO2 and N2 Capture in Reline, a Prototypical Deep Eutectic Solvent.

Deep eutectic solvents such as reline are an emerging class of low-cost, environmentally friendly solvents with tunable properties that are potentially applicable for the capture and separation of CO2. Experimental measurements showed that a reline-based membrane contactor can capture and separate CO2 via physisorption through a dissolution process with 96.7% purity from a mixed gas containing CO2 and N2 (50:50% molar ratio). We examine the nature of the interaction of CO2 and N2 with reline employing quantum chemical methods. We focus on explaining the mechanism by which CO2 and N2 bind to reline and the reason for the high selectivity for absorption of CO2 compared to N2. We analyze the dynamics, energetics, and binding motifs for CO2 and N2 in reline employing density functional theory, density functional tight binding, and ab initio molecular dynamics. We also investigate the effect of reline on the vibrational spectra of CO2 and reline. Our simulations indicate that the selective capture of CO2 from the mixture of CO2 and N2 is due to the interplay between attractive electrostatic and charge polarization forces with opposing entropic effects, which shift the energetic balance and make the N2 absorption unfavorable in reline.

Fast and succinct population protocols for Presburger arithmetic

In their 2006 seminal paper in Distributed Computing, Angluin et al. present a construction that, given any Presburger predicate, outputs a leaderless population protocol that decides the predicate. The protocol for a predicate of size m runs in O(m⋅n2log⁡n) expected number of interactions, which is almost optimal in n, the number of interacting agents. However, the number of states is exponential in m. Blondin et al. presented at STACS 2020 another construction that produces protocols with a polynomial number of states, but exponential expected number of interactions. We present a construction that produces protocols with O(m) states that run in expected O(m7⋅n2) interactions, optimal in n, for all inputs of size Ω(m). For this, we introduce population computers, a generalization of population protocols, and show that our computers for Presburger predicates can be translated into fast and succinct population protocols.

Plasma-Catalytic Methane Pyrolysis for Hydrogen and Valuable Carbons

Current technologies for hydrogen production are based primarily on reforming of fossil fuels using steam, which produces large amount of carbon dioxide emissions (> 9 tons of CO2 per ton of hydrogen produced). Majority of refineries, ammonia producers, and fuel cell power plants utilize steam methane reforming for production of hydrogen at scale.In this paper, we discuss an approach for activating methane and pyrolyzing using molten metal based alloys that includes Gallium. Sunkara’s group had developed this process earlier for making carbon micro-tubes with tunable morphology.[1, 2] Here, experiments were performed using pure methane, acetylene suggests a potential pathway for complete pyrolysis through recycle to produce hydrogen and carbons. The carbons produced are high surface area and are also do not contain any impurities. Majority of the carbons produced contain graphene sheets in random manner along with onion morphologies.The mechanism of methane pyrolysis involves a similar mechanism as that of silicon dissolution from silanes into molten Gallium. The activated species dissolve into molten Ga [3] and then undergo dehydrogenation reactions resulting in carbon nucleation and growth on molten Ga surface. The immiscibility of carbon and molten Ga allows for easier separation of resulting carbons through simple scraping from the surface.Techno-economic analysis suggests that the cost of hydrogen produced using the proposed catalytic technology could be less than $1/kg if the carbon by-product has value > $3/kg. Such low cost of hydrogen production is only possible if the following technical specifications are met: methane conversion is greater than 90%; scalable to 100 tons per year; and reduced loss and re-use of catalyst. Bhimarasetti, G., J.M. Cowley, and M.K. Sunkara, Carbon microtubes: tuning internal diameters and conical angles. Nanotechnology, 2005. 16(7): p. S362. Bhimarasetti, G., et al., Morphological Control of Tapered and Multi‐Junctioned Carbon Tubular Structures.Advanced Materials, 2003. 15(19): p. 1629-1632. Carreon, M.L., et al., Synergistic interactions of H2 and N2 with molten gallium in the presence of plasma. Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2018. 36(2): p. 021303.

Plasma‐Driven Nitrogen Fixation on Sodium Hydride

AbstractThe development of alternative approaches to the conventional Haber–Bosch ammonia synthesis process is an imperative but very challenging task. Extrinsic stimuli such as plasma could provide greater flexibility in materials selection and process innovation for nitrogen fixation. Hydride (hydrogen anion, H‾)‐containing materials have recently shown promise in thermal ammonia synthesis, whereas the interactions of hydrides and N2 under plasma have rarely been investigated. Herein we explore plasma‐driven nitrogen fixation to NH3 mediated by an inexpensive and common reagent sodium hydride, which does not react with N2 under normal thermal conditions. Nitrogen plasma can produce reactive nitrogen species and also induce the dehydriding of NaH, which result in the activation and hydrogenation of N2 to surface NaNH2 species. The subsequent thermal‐hydrogenation of NaNH2 produces NH3 facilely. The stepwise chemical loop prevents ammonia from plasma‐induced cracking. This NaH‐mediated chemistry broadens the scope of hydrides as well as many other materials for N2 fixation, and also has prospect for other chemical transformations.

Adsorption mechanism of the N2 and NRR intermediates on oxygen modified MnN4-graphene layers - a single atom catalysis perspective.

In the present work the adsorption of N2 and the nitrogen reduction reaction (NRR) intermediates have been investigated on oxygen modified MnNxOy (x + y = 4, x ≠ 0)/graphene layers through periodic density functional theory calculations. Various number of oxygen atoms substitute nitrogen atoms within the MnNxOy, with their effect on the layer stability, chemical bonding and N2 adsorption being explored. As the oxygen amount increases in the porphyrin unit, Mn-O interactions weaken with reference to that of Mn-N, bonding orbitals become less populated while the antibonding orbitals between Mn-N-O atoms become partially occupied, as evidenced by the Crystal orbital Hamiltonian population (COHP) and integrated crystal orbital bond index (ICOBI) analyses. During N2 adsorption on the different layers, the substitution of two and three nitrogen atoms by oxygen leads to the longest NN molecular bond length. Two main orientations for the N2 molecules sorption have been investigated: side-on and end-on which are perpendicular and parallel to the surface normal, respectively. When the interaction of N2 with MnNO3 layer is considered, d-band center variation of the Mn with reference to the pre-adsorbed state is more obvious after side-on adsorption configuration. For the selected layers based on initial N2 adsorption energies, the adsorption energies of nitrogen reduction reaction intermediates follow a trend based on the number of oxygen atoms in the porphyrin units. Charge density difference (CDD) maps and partial density of states (PDOS) analysis reveal that the interaction of N2 with oxygen modified layers takes place through electron acception-donation mechanism between the partially occupied Mn-d orbitals and the 2p orbitals of the N2 molecule. DDEC6-derived bond orders and atomic charges support the PDOS and adsorption/formation energy trends, and further clarify the bonding strengths of the atoms in the porphyrin units, as well as the Mn-N2 interactions in the adsorbed systems.

Mechanistic understanding of N2 activation: a comparison of unsupported and supported Ru catalysts.

N2 dissociative adsorption is commonly the rate-determining step in thermal ammonia synthesis. Herein, we performed density functional theory (DFT) calculations to understand the N2 dissociation mechanism on models of unsupported Ru(0001) terraces, Ru B5 sites, and polar MgO(111)-supported Ru8 cluster mimicking a B5 site geometry, denoted (Ru8(B5-like)/MgO(111)). The activation energy of N2 dissociative adsorption on the Ru8(B5-like)/MgO(111) model (Ea = 0.33 eV) is much lower than that on the unsupported Ru(0001) terrace (Ea = 1.74 eV) and Ru B5 (Ea = 0.62 eV) models. The lower N2 dissociation barrier on Ru B5 sites is facilitated by the enhanced σ donation and π* back-donation between N2(σ, π*) and Ru(d) orbitals resulting in the stronger activation of the molecular side-on N2* dissociation precursor. The Ru8(B5-like)/MgO(111) also exhibits enhanced σ donation because of the B5-like cluster geometry. Furthermore, the Ru cluster of the bare Ru8(B5-like)/MgO(111) model is positively charged. This induced an unusual π donation from N2(π) to Ru(d) orbitals as revealed by analyses of the density of states and partial charge densities. The combined σ and π donation resulted in an increased synergistic π* back-donation. The total interactions between N2(σ, π, π*) and Ru(d) resulted in an overall electron transfer to the adsorbed N2 from the Ru atoms in the B5-like site with no direct involvement of the MgO(111) substrate. Analyses of bond stretching vibrations and bond lengths show that the N2(σ, π, π*) and Ru(d) interactions lead to a weaker N-N bond and stronger Ru-N bonds. These correspond to a lower barrier of N2 dissociation on the Ru8(B5-like)/MgO(111) model, where the highest red-shift of N-N vibration and the longest N-N bond length were observed after side-on N2* adsorption. These results demonstrate that an electron-deficient Ru catalyst are not always inhibited from donating electrons to adsorbed N2. Rather, this study shows that the electron deficiency of Ru can promote π* back-donation and N2 activation. These new insights may therefore open new avenues to design supported Ru catalysts for nitrogen activation.

ONIOM2-DFT study of N2, O2 and NO interaction with Ce-MOR: Active sites and thermodynamics

A theoretical study was carried out for the adsorption of N2, O2, NO and NO+ with Cerium (Ce) modified mordenite (MOR). A two-layer ONIOM2 (two layer Integrated molecular Orbital + molecular Mechanics) methodology was employed, combining UFF (Universal Force Field) and DFT (Density Functional Theory) calculations for the low and high level, respectively. The formation of active Ce species based on the adsorption of CeO+ on the crystallographic positions T1, T2 and T4 in the H-MOR was studied. The geometrical, vibrational and thermodynamic results indicate that the Ce atom of CeO+ binds exothermically and spontaneously to two of the non-equivalent (Om) crystallographic oxygens of MOR (TnOm1Om2) according to: T1O1O4, T1O2O3, T2O4O7, T2O5O7 and T4O7O10 (T: Al or Si). The results of the interaction of N2, O2, NO and NO+ with Ce-MOR indicate that only exothermic and spontaneous adsorptions occur on the active sites located over the main channel of the 12-membered ring (12-MR) according to T1O1O4, T2O5O7 and T4O7O10. In general, the Ce-MOR system stabilizes electrophilic [CeO(NO+)] species, with possible activity deNOx reactions in the presence of nucleophilic reductants such as NH3; while for CeO(NO) species adsorbed on MOR a dynamic equilibrium between κ1NO, κ1ON, κ2NO adsorptions is reported which could be applicable for deNOx catalysis in the absence of reductants. On the basis of thermodynamic reaction functions, it is proposed that the most likely site for the location of active CeO+ is T2O5O7.

Interaction of molecular nitrogen with vanadium oxide in the absence and presence of water vapor at room temperature: Near-ambient pressure XPS.

Interactions of N2 at oxide surfaces are important for understanding electrocatalytic nitrogen reduction reaction (NRR) mechanisms. Interactions of N2 at the polycrystalline vanadium oxide/vapor interface were monitored at room temperature and total pressures up to 10-1 Torr using Near-Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS). The oxide film was predominantly V(IV), with V(III) and V(V) components. XPS spectra were acquired in environments of both pure N2 and equal pressures of N2 and H2O vapor. In pure N2, broad, partially resolved N1s features were observed at binding energies of 401.0 and 398.7eV, with a relative intensity of ∼3:1, respectively. These features remained upon subsequent pumpdown to 10-9 Torr. The observed maximum N surface coverage was ∼1.5 × 1013cm-2-a fraction of a monolayer. In the presence of equal pressures of H2O, the adsorbed N intensity at 10-1 Torr is ∼25% of that observed in the absence of H2O. The formation of molecularly adsorbed H2O was also observed. Density functional theory-based calculations suggest favorable absorption energies for N2 bonding to both V(IV) and V(III) cation sites but less so for V(V) sites. Hartree-Fock-based cluster calculations for N2-V end-on adsorption show that experimental XPS doublet features are consistent with the calculated shake-up and normal, final ionic configurations for N2 end-on bonding to V(III) sites but not V(IV) sites. The XPS spectra of vanadium oxide transferred in situ between electrochemical and UHV environments indicate that the oxide surfaces studied here are stable upon exposure to the electrolyte under NRR-relevant conditions.

Electron–N2 interactions in RF E × B fields

This study reports on rate coefficient data for excitation of electronic states and ionization of N2 molecules by electrons exposed to mutually perpendicular radio frequency electric and magnetic fields. These quantities were obtained by means of a Monte Carlo simulation, which provides mean electron energies and corresponding energy distributions within one oscillation of the external fields. The time-resolved mean electron energies and rate coefficients as well as their period averaged values are presented. Calculations were performed for different field frequencies, including one of the standard frequencies in the industrial use, 13.56 MHz, and for effective reduced electric field values of 300 and 500 Td, while the effective reduced magnetic field was varied up to 2000 Hx. The fundamental aspect of the obtained results is discussed, which is followed by a collection of tabular data for their eventual use in future models of inductively coupled N2 plasma sources.

Computational Screening of Physical Solvents for CO2 Pre-combustion Capture.

A computational scheme was used to screen physical solvents for CO2 pre-combustion capture by integrating the commercial NIST database, an in-house computational database, chem-informatics, and molecular modeling. A commercially available screened hydrophobic solvent, diethyl sebacate, was identified from the screening with favorable physical properties and promising absorption performance. The promising performance to use diethyl sebacate in CO2 pre-combustion capture has also been confirmed from experiments. Water loading in diethyl sebacate is very low, and therefore, water is kept with H2 in the gas stream. The favorable CO2 interaction with diethyl sebacate and the intermediate solvent free volume fraction leads to both high CO2 solubility and high CO2/H2 solubility selectivity in diethyl sebacate. An in-house NETL computational database was built to characterize CO2, H2, N2, and H2O interactions with 202 different chemical functional groups. It was found that 13% of the functional groups belong to the strong interaction category with the CO2 interaction energy between -15 and -21 kJ/mol; 62% of the functional groups interact intermediately with CO2 (-8 to -15 kJ/mol). The remaining 25% of functional groups interact weakly with CO2 (below -8 kJ/mol). In addition, calculations show that CO2 interactions with the functional groups are stronger than N2 and H2 interactions but are weaker than H2O interactions. The CO2 and H2O interactions with the same functional groups exhibit a very strong linear positive correlation coefficient of 0.92. The relationship between CO2 and H2 gas solubilities and solvent fractional free volume (FFV) has been systematically studied for seven solvents at 298.2 K. A skewed bell-shaped relation was obtained between CO2 solubility and solvent FFV. When an organic compound has a density approximately 10% lower than its density at 298.2 K and 1 bar, it exhibits the highest CO2 loading at that specific solvent density and FFV. Note that the solvent densities were varied using simulations, which are difficult to be obtained from the experiment. In contrast, H2 solubility results exhibit an almost perfect positive linear correlation with the solvent FFV. The theoretical maximum and minimum physical CO2 solubilities in any organic compound at 298.2 K were estimated to be 11 and 0.4 mol/MPa L, respectively. An examination of 182 experimental CO2 physical solubility data and 29 simulated CO2 physical solubilities shows that all the CO2 physical solubility data are within the maximum and minimum with only a few exceptions. Finally, simulations suggest that in order to develop physical solvents with both high CO2 solubility and high CO2/H2 solubility selectivity, the solvents should contain functional groups which are available to interact strongly with CO2 while minimizing FFV.

Molecular simulation of flows in thermochemical non-equilibrium around a cylinder using ab initio potential energy surfaces for N2 + N and N2 + N2 interactions

We present two-dimensional direct molecular simulation (DMS) results for high-enthalpy nitrogen flows in thermochemical non-equilibrium around a circular cylinder. The simulations are carried out using accurate ab initio potential energy surfaces (PES) to describe N2 + N and N2 + N2 interactions. Select comparisons with the direct simulation Monte Carlo method are presented to demonstrate how the high-fidelity DMS data, both at the level of bulk flow quantities and local molecular distributions, can be used to thoroughly inform or validate simplified reduced-order descriptions. Then, a partially dissociated nitrogen flow around a circular cylinder is obtained from two successive refinements of a well-established ab initio nitrogen PES. The only input in both calculations is the respective PESs, all other simulation parameters being precisely equal. This work, enabled by large scale computing, represents the first attempt at establishing a rigorous methodology for (i) the validation of lower-fidelity, computationally efficient models using ab initio, assumption-free calculations (DMS) as benchmarks and (ii) a systematic assessment of ab initio PES accuracy using entire flow field results.

A multi-scale algorithm for dislocation creep at elevated temperatures

Dislocation creep at elevated temperatures plays an important role for plastic deformation in crystalline metals. When using traditional discrete dislocation dynamics (DDD) to capture this process, we often need to update the forces on N dislocations involving ~N2 interactions. In this letter, we introduce a multi-scale algorithm to speed up the calculations by dividing a sample of interest into sub-domain grids: dislocations within a characteristic area interact following the conventional way, but their interaction with dislocations in other grids are simplified by lumping all dislocations in another grid as a super one. Such a multi-scale algorithm lowers the computational load to ~N1.5. We employed this algorithm to model dislocation creep in Al-Mg alloy. The simulation leads to a power-law creep rate in consistent with experimental observations. The stress exponent of the power-law creep is a resultant of dislocations climb for ~5 and viscous dislocations glide for ~3.

Resonance scattering of positronium atoms by nitrogen molecules

We study theoretically the resonance scattering of positronium (Ps) atoms by nitrogen molecules and compare it with resonance e–N2 scattering in the Πg symmetry. The velocity positions of the Ps–N2 resonances in Σu, Πu, and Δg symmetries are very close to the velocity position of the e–N2 resonance which leads to the total Ps–N2 cross section being very similar to the e–N2 cross section when both are plotted as functions of the projectile velocity. However, in the Ps–N2 case the resonances are much wider and their positions vary much slower with increasing internuclear separation than in the e–N2 case. This makes the Ps-impact vibrational excitation cross section much smaller than the electron-impact vibrational excitation cross section, and no boomerang oscillations are observed in Ps–N2 scattering. We analyze the role of the static potential in the e–N2 case and compare exchange potentials for e–N2 and Ps–N2 interactions. This analysis allows us to explain the difference in the vibrational dynamics in these two cases.

Structural Basis of Staphylococcus aureus Surface Protein SdrC.

Staphylococcus aureus surface proteins play important roles in host tissue colonization, biofilm formation, and bacterial virulence and are thus essential for successful host infections. The surface protein SdrC from S. aureus induces bacterial biofilm formation via an intermolecular homophilic interaction of its N2 domains. However, the molecular mechanism of how the homophilic interaction is achieved is unknown. Here, we report two crystal structures of SdrC N2N3 domains, revealing two possible homophilic interaction mechanisms: Ca2+-mediated intermolecular metal chelation of N2 domains and intermolecular interaction of N2 and N3 domains. Given the unnecessary role of the N3 domain in the induction of biofilm formation, the N2 domain-mediated metal chelation mechanism is likely the mechanism that facilitates SdrC homophilic interaction. Mutation of key Ca2+-chelating residues differentially reduced the level of protein dimer formation, further supporting the key role of metal chelation in the N2 domain interaction. Together, these results reveal the possible mechanism of the homophilic interaction of SdrC N2 domains and pave the way for the rational development of new strategies against this mechanism.