Periodic DFT calculations to compute the attributes of a quantum material: honeycomb ruthenium trichloride.

Quantum spin liquids (QSLs) have become prominent materials of interest in the pursuit of fault-tolerant materials for quantum computing applications. This is due to the fact that these materials are theorized to host an interesting variety of quantum phenomena such as quasi-particles that may behave as anyons as a result of the high entangled nature of the spin states within the systems. Computing the electronic and magnetic properties of these materials is necessary in order to understand the underlying interactions of the materials. In this paper, the structural, electronic, and magnetic properties including lattice parameters, bandgap, Heisenberg coupling constants, and Curie temperatures for α-RuCl3, a promising candidate for the Kitaev QSL model, are computed using periodic density functional theory. Furthermore, various parameters of the calculations (i.e. functional choice, basis set, k-point density, and Hubbard correction) are varied in order to determine what effect, if any, the computational setup has on the computed properties. The results of this study indicate that PBE functional with Hubbard corrections of 1.5-2.5 eV with a k-point density of 3.0 points per Å-1 appear to be the best parameters to compute Heisenberg coupling constants for α-RuCl3. These parameters with the addition of spin orbit coupling works well for computing Curie temperatures for α-RuCl3. Distinct differences are noted in the computations of the bulk structure vs. monolayer structures, indicating that interactions between the layers play a role in the material properties and changes to the inter-layer spacing may result in interesting and unique magnetic properties that require further investigation.

Effect of Concrete Composition on the Thermodynamic Binding of Dopamine: A DFT Study.

Concrete has long been a standard in construction projects. However, increasing the binding of cement paste to the concrete aggregate (a collection of geological materials containing, e.g., gravel, sand, etc.) remains an open area of research, as this is a common failure point in concrete-based infrastructure. One solution is the application of an adhesive into the mix that not only is capable of binding under aqueous conditions but can aid in the binding of the aggregate to the cement paste. Bioinspired catecholic-type molecules have been shown to be an ultrastrong adhesive, even under wet conditions, and would, in principle, be an ideal candidate to use. In this study, we examine how dopamine (a molecule with a catechol functionality) binds to various oxides found in concrete mixtures. We find that dopamine binds preferentially to alkaline earth oxides; thus, for concrete mixtures rich in these minerals dopamine would be an ideal candidate for improved adhesion.

Preferential Adsorption of Prominent Amino Acids in the Urease Enzyme of Sporosarcina pasteurii on Arid Soil Components: A Periodic DFT Study.

The urease enzyme is commonly used in microbially induced carbonate precipitation (MICP) and enzyme-induced carbonate precipitation (EICP) to heal and strengthen soil. Improving our understanding of the adsorption of the urease enzyme with various soil surfaces can lead to advancements in the MICP and EICP engineering methods as well as other areas of soil science. In this work, we use density functional theory (DFT) to investigate the urease enzyme's binding ability with four common arid soil components: quartz, corundum, albite, and hematite. As the urease enzyme cannot directly be simulated with DFT due to its size, the amino acids comprising at least 5% of the urease enzyme were simulated instead. An adsorption model incorporating the Gibbs free energy was used to determine the existence of amino acid-mineral binding modes. It was found that the nine simulated amino acids bind preferentially to the different soil components. Alanine favors corundum, glycine and threonine favor hematite, and aspartic acid favors albite. It was found that, under the standard environmental conditions considered here, amino acid binding to quartz is unfavorable. In the polymeric form where the side chains would dominate the binding interactions, hematite favors aspartic acid through its R-OH group and corundum favors glutamic acid through its R-Ket group. Overall, our model predicts that the urease enzyme produced by Sporosarcina pasteurii can bind to various oxides found in arid soil through its alanine, glycine, aspartic/glutamic acid, or threonine residues.

Properties and Mechanisms for PFAS Adsorption to Aqueous Clay and Humic Soil Components.

The proliferation of poly- and perfluorinated alkyl substances (PFASs) has resulted in global concerns over contamination and bioaccumulation. PFAS compounds tend to remain in the environment indefinitely, and research is needed to elucidate the ultimate fate of these molecules. We have investigated the model humic substance and model clay surfaces as a potential environmental sink for the adsorption and retention of three representative PFAS molecules with varying chain length and head groups. Utilizing molecular dynamics simulation, we quantify the ability of pyrophyllite and the humic substance to favorably adsorb these PFAS molecules from aqueous solution. We have observed that the hydrophobic nature of the pyrophyllite surface makes the material well suited for the sorption of medium- and long-tail PFAS moieties. Similarly, we find a preference for the formation of a monolayer on the surface for long-chain PFAS molecules at high concentration. Furthermore, we discussed trends in the adsorption mechanisms for the fate and transport of these compounds, as well as potential approaches for their environmental remediation.

Computational Investigation on Interactions between Some Munition Compounds and Humic Substances.

Humic acid substances (HAs) in natural soil and sediment environments affect the retention and degradation of insensitive munition compounds and legacy high explosives (MCs): 2,4-dinitroanisole (DNAN), DNi-NH4+, N-methyl-p-nitroaniline (nMNA), 1-nitroguanidine (NQ), 3-nitro-1,2,4-triazol-5-one (NTO; neutral and anionic forms), 2,4,6-trinitrotoluene (TNT), and 1,3,5-trinitro-1,3,5-triazinane (RDX). A humic acid model compound has been considered using molecular dynamics, thermodynamic integration, and density functional theory to characterize the munition binding ability, ionization potential, and electron affinity compared to that in the water solution. Humic acids bind most compounds and act as both a sink and source for electrons. Ionization potentials suggest that HAs are more susceptible to oxidation than the MCs studied. The electron affinity of HAs is very conformation-dependent and spans the same range as the munition compounds. When HAs and MCs are complexed, the HAs tend to radicalize first, thus buffering MCs against reductive as well as oxidative attacks.

Using phosphate fertilizer to reduce emitter clogging of drip fertigation systems with high salinity water.

Phosphorous (P) fertigation with high salinity water (HSW) drip irrigation would be an effective measure to relieve soil and water pollution caused by the excessive application of P fertilizer, and achieve synergistic saving of both limited fresh water and non-renewable P resources. However, the emitter clogging issues of drip fertigation systems seriously restricts the utilization of this technology. This study proposes an approach to reduce emitter clogging in HSW drip fertigation systems by choosing the appropriate type and concentration of P fertilizer. The effects of two new types of P fertilizers (ammonium polyphosphate, APP; urea phosphate, UP), and a traditional P fertilizer (monopotassium phosphate, MKP), were assessed at three fertilization concentrations (0, 0.15, and 0.30 g/L) on the clogging behavior of four types flat emitters. The results indicated that the application of MKP aggravated the clogging of emitters in comparison with non-fertilization. While the addition of two new types of P fertilizers (APP and UP) effectively alleviated emitters clogging (the irrigation uniformity of systems increased by 26.2%-74.6%) by inhibiting the formation of carbonate, although precipitation of phosphate, silicate, and quartz increased. Moreover, under the equal application amount of P fertilizer, UP and APP were more effective in relieving clogged when applied at a low-concentration with long-term running and high-concentration with short-term running mode. The results could pave a way for reducing the pollution in agricultural production and conserving freshwater and non-renewable P resources.

Predicting the Impact of Aqueous Ions on Fate and Transport of Munition Compounds in the Environment.

A model framework for natural water has been developed using computational chemistry techniques to elucidate the interactions between solvated munition compounds and eight common ions in naturally occurring water sources. The interaction energies, residence times, coordination statistics, and surface preferences of nine munition-related compounds with each ion were evaluated. The propensity of these interactions to increase degradation of the munition compound was predicted using accelerated replica QM/MM simulations. The degradation prediction data qualitatively align with previous quantum mechanical studies. The results suggest that primary ions of interest for fate and transport modeling of munition compounds in natural waters may follow the relative importance of SO42-, Cl- ≫ HCO3-, Na+, Mg2+ > Ca2+, K+, and NH4+.

Role of Singlet Oxygen in the Degradation of Selected Insensitive Munitions Compounds: A Comprehensive, Quantum Chemical Investigation.

DNAN (2,4-dinitroanisole), NTO (3-nitro-1,2,4-triazol-5-one), and NQ (nitroguanidine) are important energetic materials used in military applications. They may find their way to the environment during manufacturing, transportation, storage, training, and disposal. A detailed investigation of possible mechanisms for reactions of the nitrocompounds with singlet oxygen, one of the potential methods for their degradation, was performed by computational study using the PCM(Pauling)/M06-2X/6-311++G(d,p) approach. Obtained results suggest that reactivity of the investigated munitions compounds toward singlet oxygen follows the order: DNAN > NTO(anion) > NQ ≫ NTO. DNAN is involved in [4 + 2]-addition with oxygen, and further formation of diepoxide or epoxyketone through diradical intermediates have been predicted. The NTO may undergo intramolecular rearrangement with formation of peroxide compound or nitrite radical elimination, and NQ may be transformed into urea.

Computational Investigation on Electronic Structures and Properties of 4,6-Bis(nitroimino)-1,3,5-triazinan-2-one: An Insensitive Munition Compound.

In order to minimize unintentional detonation, munitions researchers have focused on the development of chemical compounds that are insensitive to external stimuli while maintaining their effectiveness. Although these compounds, known as high-performance insensitive munition compounds, are promising in terms of potency and stability, their environmental impacts have either not been fully understood or are yet to be investigated. In the present research, we have performed a quantum chemical investigation on electronic structures and properties of an insensitive munition compound 4,6-bis(nitroimino)-1,3,5-triazinan-2-one (DNAM). The density functional theory using the B3LYP and M06-2X functionals and MP2 methodology were used for geometry optimization of various tautomeric forms of DNAM. The effect of bulk water solution was evaluated using the conductor-like polarizable continuum model and the density-based solvation model. Ionization potentials, electron affinities, redox properties, and p Ka values were also computed and compared with the available experimental data. These physical and chemical properties of DNAM have been discussed with regard to the varying tautomeric forms in which DNAM can exist.

DFT investigation on the adsorption of munition compounds on α-Fe2O3: similarity and differences with α-Al2O3.

Arid environments have long been a testing and training ground for novel munitions. However, these activities leave behind unknown quantities of munition residues with unknown impact on local flora and fauna. In particular, arid soil contains Lewis acidic metal oxides which bind and catalyze the electron rich substituent groups commonly found in munition compounds, although the exact mechanisms are poorly understood. The current study remedies this lack of knowledge by utilizing density functional theory (DFT) to explore various orientations of four important munition compounds on the α-Fe2O3(0001) and α-Al2O3(0001) surfaces. Our findings reveal that while α-Fe2O3 binds the munition compounds more strongly than α-Al2O3, all four compounds experienced elongation of their nitro (-NO2) groups, indicating their susceptibility towards degradation on these surfaces.

Role of Stone-Wales defects on the interfacial interactions among graphene, carbon nanotubes, and Nylon 6: A first-principles study.

We investigate computationally the role of Stone-Wales (SW) defects on the interfacial interactions among graphene, carbon nanotubes (CNTs), and Nylon 6 using density functional theory (DFT) and the empirical force-field. Our first-principles DFT calculations were performed using the Quantum ESPRESSO electronic structure code with the highly accurate van der Waals functional (vdW-DF2). Both pristine and SW-defected carbon nanomaterials were investigated. The computed results show that the presence of SW defects on CNTs weakens the CNT-graphene interactions. Our result that CNT-graphene interaction is much stronger than CNT-CNT interaction indicates that graphene would be able to promote the dispersion of CNTs in the polymer matrix. Our results demonstrate that carbon nanomaterials form stable complexes with Nylon 6 and that the van der Waals interactions, as revealed by the electronic charge density difference maps, play a key stabilizing role on the interfacial interactions among graphene, CNTs, and Nylon 6. Using the density of states calculations, we observed that the bandgaps of graphene and CNTs were not significantly modified due to their interactions with Nylon 6. The Young's moduli of complexes were found to be the averages of the moduli of their individual constituents.

An integrated theoretical and experimental investigation of insensitive munition compounds adsorption on cellulose, cellulose triacetate, chitin and chitosan surfaces.

This manuscript reports results of combined computational chemistry and batch adsorption investigation of insensitive munition compounds, 2,4-dinitroanisole (DNAN), triaminotrinitrobenzene (TATB), 1,1-diamino-2,2-dinitroethene (FOX-7) and nitroguanidine (NQ), and traditional munition compound 2,4,6-trinitrotoluene (TNT) on the surfaces of cellulose, cellulose triacetate, chitin and chitosan biopolymers. Cellulose, cellulose triacetate, chitin and chitosan were modeled as trimeric form of the linear chain of 4C1 chair conformation of ß-d-glucopyranos, its triacetate form, ß-N-acetylglucosamine and D-glucosamine, respectively, in the 1➔4 linkage. Geometries were optimized at the M062X functional level of the density functional theory (DFT) using the 6-31G(d,p) basis set in the gas phase and in the bulk water solution using the conductor-like polarizable continuum model (CPCM) approach. The nature of potential energy surfaces of the optimized geometries were ascertained through the harmonic vibrational frequency analysis. The basis set superposition error (BSSE) corrected interaction energies were obtained using the 6-311G(d,p) basis set at the same theoretical level. The computed BSSE in the gas phase was used to correct interaction energy in the bulk water solution. Computed and experimental results regarding the ability of considered surfaces in adsorbing the insensitive munitions compounds are discussed.

Effect of application rate and irrigation on the movement and dissipation of indaziflam.

Indaziflam is a new preemergence herbicide for the control of annual grass and broadleaf weeds in various cropping systems including pecan orchards. The objectives of this study were to (1) determine the mobility and dissipation of indaziflam and (2) evaluate herbicide efficacy in a flood-irrigated pecan orchard in southern New Mexico, USA. Indaziflam was applied at 0, 36.5, and 73.1g/ha in areas with (impacted) and without (unimpacted) tree injury symptoms. Soil samples were collected at 0-15, 15-30, and 30-46cm depths 26, 63, 90, and 126days after the first herbicide application. Additional soil samples were collected 4, 30, and 56days after the second application. Indaziflam was detected in soil samples collected at each depth, suggesting movement with irrigation water. Indaziflam concentrations decreased with increasing soil depth and time. Indaziflam mass recoveries were greater in the unimpacted area than in the impacted area after the first and second applications. Dissipation half-lives of indaziflam in the soil ranged from 30 to 86days for total indaziflam recovered from the entire soil profile after the first and second applications in both areas. The percent weed control was similar in the impacted and unimpacted areas for both rates of indaziflam on 26 and 63days after application; however, on 90days after the application, percent weed control was lower in the impacted than unimpacted area.

Microbial and size characterization of airborne particulate matter collected on sticky tapes along US-Mexico border.

Particulate matter (PM) emissions from various sources can affect significantly human health and environmental quality especially in the Chihuahuan Desert region along US-Mexico border. The objective of this study was to use the low-cost sticky tape method to collect airborne PM for size characterization and identification of fungal spores. Sticky tape samplers were placed at 1.0 and 2.0m above the ground surface at experimental sites in Ciudad Juárez, Mexico and at 0.6, 1.2 and 1.8m at New Mexico sites, USA. Soil samples were collected in both countries to determine fungal diversity, texture and moisture content. Dust particles collected from all of the experimental sites had a dominant texture of clay (<0.002mm). The dominant textures identified from soil samples collected from the US and Mexican sites were loam and sandy clay loam, respectively. Alternaria, Penicillium and Fusarium were frequently found funguses in the US sites while Alternaria and Aspergillus were commonly observed in the Mexican sites. The sticky tapes also showed a similar diversity of fungal microorganisms present in the airborne PM at both Mexico and US sites. Alternaria, Penicillium and Aspergillus were the three groups of airborne fungal microorganisms consistently present in the US and Mexican sites. The low-cost sticky tape method has the potential to be used for characterizing different airborne microorganisms and dust particles.

In Silico Alkaline Hydrolysis of Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine: Density Functional Theory Investigation.

HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine), an energetic material used in military applications, may be released to the environment during manufacturing, transportation, storage, training, and disposal. A detailed investigation of a possible mechanism of alkaline hydrolysis, as one of the most promising methods for HMX remediation, was performed by computational study at PCM(Pauling)/M06-2X/6-311++G(d,p) level. Obtained results suggest that HMX hydrolysis at pH 10 represents a highly exothermic multistep process involving initial deprotonation and nitrite elimination, hydroxide attachment accompanied by cycle cleavage, and further decomposition of cycle-opened intermediate to the products caused by a series of C-N bond ruptures, hydroxide attachments, and proton transfers. Computationally predicted products of HMX hydrolysis such as nitrite, 4-nitro-2,4-diazabutanal, formaldehyde, nitrous oxide, formate, and ammonia correspond to experimentally observed species. Based on computed reaction pathways for HMX decomposition by alkaline hydrolysis, the kinetics of the entire process was modeled. Very low efficiency of this reaction at pH 10 was observed. Computations predict significant increases (orders of magnitude) of the hydrolysis rate for hydrolysis reactions undertaken at pH 11, 12, and 13.

Adsorption of Emerging Munitions Contaminants on Cellulose Surface: A Combined Theoretical and Experimental Investigation.

This manuscript reports results of an integrated theoretical and experimental investigation of adsorption of two emerging contaminants (DNAN and FOX-7) and legacy compound TNT on cellulose surface. Cellulose was modeled as trimeric form of the linear chain of 1 â†’ 4 linked of ß-D-glucopyranos in (4)C1 chair conformation. Geometries of modeled cellulose, munitions compounds and their complexes were optimized at the M06-2X functional level of Density Functional Theory using the 6-31G(d,p) basis set in gas phase and in water solution. The effect of water solution was modeled using the CPCM approach. Nature of potential energy surfaces was ascertained through harmonic vibrational frequency analysis. Interaction energies were corrected for basis set superposition error and the 6-311G(d,p) basis set was used. Molecular electrostatic potential mapping was performed to understand the reactivity of the investigated systems. It was predicted that adsorbates will be weakly adsorbed on the cellulose surface in water solution than in the gas phase.

Plane-wave density functional theory investigation of adsorption of 2,4,6-trinitrotoluene on Al-hydroxylated (0001) surface of (4 × 4) α-alumina.

This article reports the results of the theoretical investigation of adsorption of 2,4,6-trinitrotoluene (TNT) on Al-hydroxylated (0001) surface of (4 × 4) α-alumina (α-Al2O3) using plane-wave Density Functional Theory. Sixteen water molecules were used to hydroxylate the alumina surface. The Perdew-Burke-Ernzerhof functional and the recently developed van der Waals functional (vdW-DF2) were used. The interaction of electron with core was accounted using the Vanderbilt ultrasoft pseudopotentials. It was found that hydroxylation has significant influence on the geometry of alumina and such changes are prominent up to few layers from the surface. Particularly, due to the Al-hydroxylation the oxygen layers are decomposed into sublayers and such partitioning becomes progressively weaker for interior layers. Moreover, the nature of TNT adsorption interaction is changed from covalent type on the pristine alumina surface to hydrogen-bonding interaction on the Al-hydroxylated alumina surface. TNT in parallel orientation forms several hydrogen bonds compared to that in the perpendicular orientation with hydroxyl groups of the Al-hydroxylated alumina surface. Therefore, the parallel orientation will be present in the adsorption of TNT on Al-hydroxylated (0001) surface of α-alumina. Further, the vdW-DF2 van der Waals functional was found to be most suitable and should be used for such surface adsorption investigation.

Reaction mechanisms for methyl isocyanate (CH3NCO) gas-phase degradation.

Methyl isocyanate (MIC) is a toxic chemical found in many commercial, industrial, and agricultural processes, and was the primary chemical involved in the Bhopal, India disaster of 1984. The atmospheric environmental chemical reactivity of MIC is relatively unknown with only proposed reaction channels, mainly involving OH-initiated reactions. The gas-phase degradation reaction pathways of MIC and its primary product, formyl isocyanate (FIC), were investigated with quantum mechanical (QM) calculations to assess the fate of the toxic chemical and its primary transformation products. Transition state energy barriers and reaction energetics were evaluated for thermolysis/pyrolysis-like reactions and bimolecular reactions initiated by relevant radicals (•OH and Cl•) to evaluate the potential energy surfaces and identify the primary reaction pathways and products. Thermolysis/pyrolysis of MIC requires high energy to initiate N-CH3 and C-H bond dissociation and is unlikely to dissociate except under extreme conditions. Bimolecular radical addition and H-abstraction reaction pathways are deemed the most kinetically and thermodynamically favorable mechanisms. The primary transformation products of MIC were identified as FIC, methylcarbamic acid, isocyanic acid (isocyanate radical), and carbon dioxide. The results of this work inform the gas-phase reaction channels of MIC and FIC reactivity and identify transformation products under various reaction conditions.

Micromechanical Dilution of PLA/PETG-Glass/Iron Nanocomposites: A More Efficient Molecular Dynamics Approach.

Polylactic acid (PLA) and poly(ethylene terephthalate glycol) (PETG) are popular thermoplastics used in additive manufacturing applications. The mechanical properties of PLA and PETG can be significantly improved by introducing fillers, such as glass and iron nanoparticles (NPs), into the polymer matrix. Molecular dynamics (MD) simulations with the reactive INTERFACE force field were used to predict the mechanical responses of neat PLA/PETG and PLA-glass/iron and PETG-glass/iron nanocomposites with relatively high loadings of glass/iron NPs. We found that the iron and glass NPs significantly increased the elastic moduli of the PLA matrix, while the PETG matrix exhibited modest increases in elastic moduli. This difference in reinforcement ability may be due to the slightly greater attraction between the glass/iron NP and PLA matrix. The NASA Multiscale Analysis Tool was used to predict the mechanical response across a range of volume percent glass/iron filler by using only the neat and highly loaded MD predictions as input. This provides a faster and more efficient approach than creating multiple MD models per volume percent per polymer/filler combination. To validate the micromechanics predictions, experimental samples incorporating hollow glass microspheres (MS) and carbonyl iron particles (CIP) into PLA/PETG were developed and tested for elastic modulus. The CIP produced a larger reinforcement in elastic modulus than the MS, with similar increases in elastic modulus between PLA/CIP and PETG/CIP at 7.77 vol % CIP. The micromechanics-based mechanical predictions compare excellently with the experimental values, validating the integrated micromechanical/MD simulation-based approach.

Exploration of functionalizing graphene and the subsequent impact on PFAS adsorption capabilities via molecular dynamics.

Per- and polyfluoroalkyl substances (PFAS) are extremely stable compounds due to their strong C-F bonds. They are used in water and stain proof coatings, aqueous film forming foams for fire suppression, cosmetics, paints, adhesives, etc. PFAS have been found in soils and waterways around the world due to their widespread usage and recalcitrance to degradation. Development of selective adsorbent materials is necessary to effectively capture a vast family of PFAS structures in order to remediate PFAS contamination in the environment. The work herein is focused on extracting design principles from molecular dynamics simulations of PFAS with functionalized graphene materials. Simulations examined how PFBA, PFOA, and PFOS interact with graphene, graphene oxide, nitrogen group-functionalized graphene oxide, partially fluorinated graphene flakes, and fully fluorinated flakes. Five flakes were used in each simulation to examine how interactions between flakes may lead to competitive interactions with respect to PFAS or formation of pores. Our study revealed that both the clustering mechanisms of the flakes and functional groups on the flake play a role in PFAS adsorption. The most effective functionalizations for PFAS adsorption are as follows: pristine graphene ≈ fully fluorinated > graphene oxide ≈ partially fluorinated > amine and amide functionalized graphene oxide flake. Long chain PFAS and sulfonate PFAS had higher propensity to adsorb to the materials compared to short chain PFAS and carboxylic head groups.