Monte Carlo Theory Research Articles

Guided Heterostructure Growth of CoFe LDH on Ti3C2Tx MXene for Durably High Oxygen Evolution Activity.

Heterostructures of layered double hydroxides (LDHs) and MXenes have shown great promise for oxygen evolution reaction (OER) catalysts, owing to their complementary physical properties. Coupling LDHs with MXenes can potentially enhance their conductivity, stability, and OER activity. In this work, a scalable and straightforward in situ guided growth of CoFeLDH on Ti3C2Tx is introduced, where the surface chemistry of Ti3C2Tx dominates the resulting heterostructures, allowing tunable crystal domain sizes of LDHs. Combined simulation results of Monte Carlo and density functional theory (DFT) validate this guided growth mechanism. Through this way, the optimized heterostructures allow the highest OER activity of the overpotential = 301mV and Tafel slope = 43mV dec-1 at 10mA cm-2, and a considerably durable stability of 0.1% decay over 200h use, remarkably outperforming all reported LDHs-MXenes materials. DFT calculations indicate that the charge transfer in heterostructures can decrease the rate-limiting energy barrier for OER, facilitating OER activity. The combined experimental and theoretical efforts identify the participation role of MXene in heterostructures for OER reactions, providing insights into designing advanced heterostructures for robust OER electrocatalysis.

Using ligand regulation, metal replacement, and ligand doping strategies on Zr-FUM to improve methane separation from coalbed gas

Developing adsorbents suitable for industrial applications that can effectively enhance the separation of methane (CH4) from nitrogen (N2) in coalbed gas is crucial to improve energy recovery and mitigate greenhouse gas emissions. In this study, three modification strategies were implemented on Zr-FUM, including ligand regulation, metal replacement, and ligand doping, to synthesize Zr-FDCA, Al-FUM, and Zr-FUM-FA, with the aim of improving the performance of CH4/N2 separation under humid conditions. The results demonstrated that the promotion of robust orbital overlap and strengthened electrovalent bonding on adsorbents can selectively enhance CH4 adsorption. As a result, Zr-FUM-FA achieved a saturated CH4 adsorption capacity of 1.37 mmol/g, a CH4 working window of 307 s, and a CH4/N2 sorbent selection parameter (Ssp) of 47.31, exceeding the performance of most reported adsorbents. Analyses of the pore structure, surface morphology, and functional groups revealed that the presence of an ultramicropore proximity to CH4, reduced static resistance, and enhanced electrovalent bond were key factors for CH4 separation. Grand Canonical Monte Carlo and Density Functional Theory studies indicated that the introduction of -C-H- in FA played a crucial role in enhancing CH4 adsorption. Optimization of adsorption parameters using the Aspen adsorption package showed that in a dual-adsorbent bed system, the recovery and purity of CH4 in Zr-FUM-FA reach 99.5% and 97.3%, respectively, providing important theoretical support for the improvement of CH4 recovery in the pressure swing adsorption process from coalbed gas.

Theoretical investigation of mixed-metal metal-organic frameworks as H2 adsorbents: insights from GCMC and DFT simulations

ABSTRACT Molecular hydrogen ( H 2 ) is a renewable energy carrier, however, its practical applications are limited due to the challenges of developing safe and efficient H 2 storage devices. Metal Organic Frameworks (MOFs) containing at least two different metal ions in their structures are called as mixed-metal MOFs (MM-MOFs) and they could adsorb H 2 in higher amounts compared to structures containing single metal nodes. We theoretically examined the H 2 storage capacities of 26 MM-MOFs having various physical and chemical properties applying Grand Canonical Monte Carlo (GCMC) and Density Functional Theory (DFT) simulations. H 2 adsorption isotherms were calculated using a five-site anisotropic H 2 model. QIXSOG, YOMVIG, OSOYUR, Cu-Mg-BTC, Fe-Mg-BTC, and Cr-Mg-BTC were selected as top-performing MM-MOFs maximising H 2 adsorption gravimetrically and volumetrically at near-ambient conditions (233 K and 100 bar), approaching the DOE targets. YOMVIG has the largest H 2 adsorption enthalpy, calculated as − 9.93 kJ/mol at 233 K and 100 bar. DFT simulations have been conducted to analyse preferable H 2 adsorption sites as well as identify guest-host interactions. Electron density difference analysis showed that adsorbed H 2 molecules in the OSOYUR, Cr-Mg-BTC, Cu-Mg-BTC, and Fe-Mg-BTC are polarised. Our study challenges existing literature by identifying promising MM-MOFs as potential next-generation hydrogen storage adsorbents at near-ambient conditions.

Application of South African heulandite (HEU) zeolite for the adsorption and removal of Pb2+ and Cd2+ ions from aqueous water solution: Experimental and computational study

The capacity of South African Heulandite (HEU) zeolite to remove Pb2+ and Cd2+ ions from aqueous solution was investigated using batch experiments and molecular simulations studies. The effect of different factors on the adsorption of these ions onto the zeolite was investigated; contact time, initial metal ion concentration and the amount of HEU adsorbent. Molecular simulations was done using Monte Carlo and density functional theory. Experimental results obtained indicate that the maximum adsorption for the two ions occur at pH 5 and after 240 min of contact time. The percent removal based on contact time of Pb2+ and Cd2+ ions from water by the heulandite zeolite were 99.7 and 76.7 %, respectively. The adsorption of two metal ions onto the HEU zeolite follows the Langmuir adsorption isotherm. From the molecular simulation findings, the adsorption of Pb2+ ions onto the HEU window is equidistant from the two adjacent oxygen atoms within the HEU structure while the Cd2+ ion is adsorbed in the upper left side of the 8-ring HEU window. It was observed that the performance of the zeolite can significantly be improved by doping with germanium, aluminum, thallium indium, and sodium cations. These results indicate that the application of HEU zeolite as an adsorbent holds a great promise in heavy metal removal from aqueous solutions.

Effect analysis of temperature and initial water content on the adsorption and separation of VOCs by ZIF‐8 based on molecular simulation

AbstractVolatile organic compounds (VOCs) have seriously polluted the atmospheric environment and caused harmful effects on human beings, so it is imperative to control oil vapor emissions. Metal organic framework materials, as one of the porous materials, have a good application prospect in the field of gas adsorption separation. In this paper, the effects of temperature and initial water content (IWC) on the adsorption properties of methane (CH4), ethane (C2H6), ethylene (C2H4), propane (C3H8), and propylene (C3H6) by ZIF‐8 were studied by combining the large gauge Monte Carlo (GCMC) and ideal adsorption solution theory. The results show that the higher the temperature is, the lower the adsorption capacity is, the higher the threshold pressure is, and the single molecule interaction energy changes little with temperature. But pore volume is still the main influencing factor. The IWC also reduces the saturated adsorption capacity. Preloaded water molecules can enhance the electrostatic interaction at low pressure, thus affecting the adsorption heat and interaction energy of single molecules. Overall, these findings provide valuable mechanistic insights into the effects of temperature and IWC on the adsorption properties of ZIF‐8 for VOCs.

Single landslide risk assessment considering rainfall‐induced landslide hazard and the vulnerability of disaster‐bearing body

Quantitative calculation of single landslide risk has great significance for the prevention and treatment of landslides, through analysing the slope stability under different rainfall recurrence periods. In this study, the rainfall of the past 40 years in Xun'wu County of China is counted and the rainfall during the return periods of 10, 20 and 50 years are calculated to form three different rainfall conditions. Then, the stability of Cheng'nan landslide in Xun'wu County is calculated by the Geo‐Studio 2007 software, and the probability of landslide occurrence is obtained by Monte Carlo theory under these three conditions. Next, the field investigation is employed to obtain the statistical results of the buildings and personnel in the affected area of Cheng'nan landslide. Finally, the risk of economic loss and casualty under the three conditions are calculated. It was demonstrated that: (1) Under the three conditions, the safety factor decreased gradually, the rate of decrease was slower in the first 3 days and faster in the middle period and there was still a downward trend after the end of the rain. (2) The probability of landslide occurrence during the rainfall return periods of 10, 20 and 50 years were 1.77%, 2.97% and 1.61%, respectively. Besides, the risk index of landslide was the highest under the condition of 20‐years rainfall return period. (3) The economic loss risk and casualty risk in the rainfall return periods of 10, 20 and 50 years were 122,700‐yuan and 4.11 people, 205,900‐yuan and 6.89 people, as well as 11,600‐yuan and 3.74 people, respectively.

STUDY OF K2SiF6:Mn4+@SiO2 PHOSPHOR FOR WHITE LEDS WITH HIGH ANGULAR COLOR UNIFORMITY

The distinctive wide-band blue illumination absorption and red strait-line discharge of the phosphor K2SiF6:Mn4+ (KMnSF) make it an attractive material for manufacturing warm white light-emitting diodes (WLED). Nevertheless, using the highly corrosive raw ingredient HF to produce commercial KMnSF red phosphor has negative effects on the environment and people. In this study, microfluidic technology was used to successfully manufacture the KMnSF without the need for HF compound while resulting in a phosphor product with homogenous granule shape and size. The luminescence capabilities of the KMnSF samples were then thoroughly examined and characterized. Eventually, we made WLED packages comprising of blue LED chips, yellow phosphor Y3Al5O12:Ce3+ (YGA:Ce), red phosphor KMnSF, and SiO2 scattering particle. Via varying the SiO2 concentration during the simulation process, the prepared WLED’s optical performances are obtained. The scattering properties of the phosphor layer as well as the lighting transmission and distribution were simulated with the utilization of both LightTools software and Monte Carlo theory. According to the outcomes, the microfluidic-synthesized K2SiF6:Mn4+ proves to be appropriate for WLED apparatuses. Besides, the proposed phosphor compound with SiO2 scattering particles showed the improvement in luminous flux and angular uniformity of the WLED.

Monte Carlo Simulation for Risk Management in ِِِAgile Software Development

Agile development methodologies are becoming increasingly popular in agile development projects due to their iterative nature and adaptability. The Monte Carlo method is distinguished by its statistical technique of using random samples to obtain many satisfactory results for solving uncertainty. It can be used in agile software development by building different scenarios and measuring their impact on the project results through statistical operations. Its ability to meet significant challenges in managing risk and uncertainty mitigation. In this study, we propose a Monte Carlo simulation-based approach to measure and analyze risks in the agile development process. It provides a probabilistic framework for risk assessment by integrating the Monte Carlo simulation methodology to model the various development process variables. It was addressed by identifying the main risk factors within agile projects, such as tasks, availability of resources, and external dependencies. The proposed approach contributes to mitigating potential risks in agile software development using Monte Carlo theory, which provides a systematic framework that enables work teams and management to overcome risk and uncertainty associated with the agile development process in dynamic project environments.

Witnessing environment induced topological phase transitions via quantum Monte Carlo and cluster perturbation theory studies

Witnessing environment induced topological phase transitions via quantum Monte Carlo and cluster perturbation theory studies

Bromine functionalization of metal–organic frameworks to improve ethane/ethylene separation

Metal–organic frameworks (MOFs) have undergone extensive study as ethane-selective adsorbents for ethane/ethylene (C2H6/C2H4) separation, a process currently conducted through energy-intensive cryogenic distillation in the petrochemical industry. Herein, we present the effect of functionalization using bromine, known for its high polarizability, on the C2H6-selective adsorption properties of MOF. This approach, based on the slightly larger polarizability of C2H6 compared to C2H4, was systematically investigated using three isostructural MOFs: DMOF-1, DMOF-1-Br, and DMOF-1-Br2, featuring 1,4-benzenedicarboxylate, 2-bromo-1,4-benzenedicarboxylate, and 2,5-dibromo-1,4-benzenedicarboxylate ligands, respectively. While their C2H6/C2H4 selectivity, based on the ideal adsorbed solution theory, increased (from 1.51 to 1.75 at 298 K and 100 kPa for the 1/1 (v/v) mixture) with the rising Br content, breakthrough experiments revealed that DMOF-1-Br achieves the highest high-purity (>99.95 %) C2H4 productivity (9.7 LSTP kg−1 at 298 K and 100 kPa for the 1/1 mixture and 22.2 LSTP kg−1 for the 1/15 mixture). This accomplishment is attributed to the appropriate bromine functionalization. Further insight into their C2H6-selective adsorption behavior was gained through canonical Monte Carlo and dispersion-corrected density functional theory simulations.

Separation of High-Purity C2H2 from Binary C2H2/CO2 Using Robust Al-Based MOFs Comprising Nitrogen-Containing Heterocyclic Dicarboxylate.

In this study, three nitrogen-containing aluminum-based metal-organic frameworks (Al-MOFs), namely, CAU-10pydc, MOF-303, and KMF-1, were investigated for the efficient separation of a C2H2/CO2 gas mixture. Among these three Al-MOFs, KMF-1 demonstrated the highest selectivity for C2H2/CO2 separation (6.31), primarily owing to its superior C2H2 uptake (7.90 mmol g-1) and lower CO2 uptake (2.82 mmol g-1) compared to that of the other two Al-MOFs. Dynamic breakthrough experiments, using an equimolar binary C2H2/CO2 gas mixture, demonstrated that KMF-1 achieved the highest separation performance. It yielded 3.42 mmol g-1 of high-purity C2H2 (>99.95%) through a straightforward desorption process under He purging at 298 K and 1 bar. To gain insights into the distinctive characteristics of the pore surfaces of structurally similar CAU-10pydc and KMF-1, we conducted computational simulations using canonical Monte Carlo and dispersion-corrected density functional theory methods. These simulations revealed that the secondary amine (C2N-H) groups in KMF-1 played a more significant role in differentiating between C2H2 and CO2 compared to that of the N atoms in CAU-10pydc and MOF-303. Consequently, KMF-1 emerged as a promising adsorbent for the separation of high-purity C2H2 from binary C2H2/CO2 gas mixtures.

Lithium-Ion Doping for Enhanced Hydrogen Sulfide Adsorption on Metal–Organic Frameworks: Grand Canonical Monte Carlo and Density Functional Theory Simulations

Lithium-Ion Doping for Enhanced Hydrogen Sulfide Adsorption on Metal–Organic Frameworks: Grand Canonical Monte Carlo and Density Functional Theory Simulations

Ultrahigh performance CO2 capture and separation in alkali metal anchored 2D-COF

The development of advanced adsorbents with high CO2 capture and separation performances is essential for decreasing atmospheric CO2 concentration. Herein, grand canonical Monte Carlo and density functional theory were employed to investigate the adsorption and separation properties of CO2, N2, and CH4 in 2D covalent organic framework (COFs) anchored by alkali metal (AMs) Li, Na, and K (UPC-nAMs, n = 3 or 6) at 298 K and 0–1.0 bar. The anchoring of AMs formed favorable adsorption sites, endowing UPC-nAMs with better CO2 capture and separation performances. This effect was more evident with an increase in Li/Na/K concentration. The CO2 adsorption capacity of UPC-6Li/Na/K was ∼ 221.64, 188.28, and 140.50 cm3 cm−3. The smaller atomic size of Li occupied less adsorption space, resulting in the highest CO2 capture capacity of 221.64 cm3 cm−3 with selectivity of 308/206 over N2/CH4 in UPC-6Li at 298 K and 1.0 bar. Structural stability, pore characteristics, isothermal adsorption heat, van der Waals and Coulomb interactions, gas distribution density, adsorption configuration, and gas radial distribution function were analyzed to identify the intrinsic mechanism of anchoring Li/Na/K to improve CO2 capture and separation performances.

Optimized equivalent linearization for random vibration

A fundamental limitation of various Equivalent Linearization Methods (ELMs) in nonlinear random vibration analysis is that they are approximate by their nature. A quantity of interest estimated from an ELM has no guarantee to be the same as the solution of the original nonlinear system. In this study, we tackle this fundamental limitation. We sequentially address the following two questions: (i) given an equivalent linear system obtained from any ELM, how to construct an estimator such that, as the linear system simulations are guided by a limited number of nonlinear system simulations, the estimator converges on the nonlinear system solution? (ii) how to construct an optimized equivalent linear system such that the estimator approaches the nonlinear system solution as quickly as possible? The first question is theoretically straightforward since classic Monte Carlo techniques, such as the control variates and importance sampling, can improve upon the solution of any surrogate model. We adapt the well-known Monte Carlo theories into the specific context of equivalent linearization. The second question is challenging, especially when rare event probabilities are of interest. We develop specialized methods to construct and optimize linear systems. In the context of uncertainty quantification (UQ), the proposed optimized ELM can be viewed as a physical surrogate model-based UQ method. The embedded physical equations endow the surrogate model with the capability to handle high-dimensional uncertainties in stochastic dynamics analysis.

Recent progress on chemical vapor deposition growth of 2D materials

Remarkable progress has been made to understand the chemical vapor deposition (CVD) of two-dimensional (2D) materials over the last two decades. The review summarized the state-of-the-art experimental synthesis and modelling and simulation on 2D materials CVD growth. Firstly, the family of 2D materials, and their CVD growth processes are introduced. Secondly, the experimental synthesis and modelling and simulation on graphene growth are discussed. In particular, the applications of reactive molecular dynamics methods, kinetic Monte Carlo and density-functional theory in 2D material growth are addressed. Then, the CVD growth of hexagonal boron nitride and transition metal dichalcogenides are further discussed, focusing on the effects of reaction conditions (growth temperature, pressure, vapour-phase composition, etc.) on the domain morphologies, edge structures and grain boundaries of 2D materials. Last, conclusions and outlooks are presented.

The role of electron correlations in the electronic structure of putative Chern magnet TbMn6Sn6

A member of the RMn6Sn6 rare-earth family materials, TbMn6Sn6, recently showed experimental signatures of the realization of a quantum-limit Chern magnet. In this work, we use quantum Monte Carlo (QMC) and density functional theory with Hubbard U (DFT + U) calculations to examine the electronic structure of TbMn6Sn6. To do so, we optimize accurate, correlation-consistent pseudopotentials for Tb and Sn using coupled-cluster and configuration–interaction (CI) methods. We find that DFT + U and single-reference QMC calculations suffer from the same overestimation of the magnetic moments as meta-GGA and hybrid density functional approximations. Our findings point to the need for improved orbitals/wavefunctions for this class of materials, such as natural orbitals from CI, or for the inclusion of multi-reference effects that capture the static correlations for an accurate prediction of magnetic properties. DFT + U with Mn magnetic moments adjusted to the experiment predict the Dirac crossing in bulk to be close to the Fermi level, within ~120 meV, in agreement with the experiments. Our non-stoichiometric slab calculations show that the Dirac crossing approaches even closer to the Fermi level, suggesting the possible realization of Chern magnetism in this limit.

Aperture Fine‐Tuning in Cage‐Like Metal–Organic Frameworks via Molecular Valve Strategy for Efficient Hexane Isomer Separation

Cage‐like metal–organic frameworks (MOFs) are promising for hexane isomer separation, but their aperture sizes are difficult to control precisely. Herein, a molecular valve strategy is proposed to fine‐tune the aperture of cage‐like MOFs, thereby enhancing their separation performance for hexane isomers. Three novel isostructural cage‐like MOFs, namely Cu‐MO4‐TPA, are synthesized using different oxometallate anions (MO42−, M = Cr, Mo, and W) and the ligand tri(pyridin‐4‐yl)amine (TPA). The different oxometallate anions induce varying degrees of twisting in the TPA ligand, leading to sub‐angstrom tuning in the aperture size of the MOFs. The materials can separate hexane isomers based on their degree of branching, with the smallest aperture material (Cu‐MoO4‐TPA) showing molecular sieving of di‐branched isomers. Adsorption isotherms, kinetic, and breakthrough measurements, Monte Carlo, and density functional theory calculations confirm the aperture size differences result in superior separation of hexane isomers by molecular sieving on Cu‐MoO4‐TPA. The results demonstrate the effectiveness of molecular valve strategy for fine‐tuning MOF aperture size for selective separation applications.

Structural Stability of Graphene-Supported Pt Layers: Diffusion Monte Carlo and Density Functional Theory Calculations

Structural Stability of Graphene-Supported Pt Layers: Diffusion Monte Carlo and Density Functional Theory Calculations

Li-decorated graphdiyne for ultrahigh-performance CO2 capture and separation over N2

The development of CO2 adsorbents with high adsorption and separation performances is important to solve severe environmental problems. Herein, two-dimensional graphdiyne acetylene rings doped with different concentrations of lithium atoms (1/2/6Li-GDYs) were introduced as potential adsorbents for CO2 capture and separation by using Grand Canonical Monte Carlo and Density Functional Theory methods. According to the structure analysis, Li atoms could stably bind to GDY with a binding energy of 1.04 – 2.77 eV/atom; 1/2/6Li-GDYs had high cohesive energy of 7.02 – 7.54 eV/atom. Electronic structure analysis confirmed the large charge transfer and strong interaction between Li atoms and GDY. The pore physical properties of Li-GDYs indicated that the pore volume, porosity, and pore size provided a favorable environment for CO2 adsorption. Among Li-GDYs, 2/6Li-GDYs exhibited an ultra-high CO2 adsorption capacity of 11.91 mmol/g at 298 K and 100 kPa, and was superior to other metal-modified adsorbents. The CO2/N2 selectivity in 1/2/6Li-GDYs reached ∼ 168, ∼311, and ∼ 1021 at 298 K and 100 kPa. Gas distribution analysis revealed a broad CO2 distribution consisting of multilayer adsorption peaks around Li and adjacent C atoms, illustrating the significant effect of Li and Li-connected C atoms on CO2 adsorption. Interaction analysis showed that Li doping enhanced the CO2-framework interaction more significantly than the N2-framework interaction, resulting in ultra-high CO2 adsorption capacity and CO2/N2 selectivity. The results of this work highlight 1/2/6Li-GDYs as ultrahigh-performance adsorbent materials for CO2 adsorption and separation over N2.

Characterization of Fast Neutron Transmission Through an Iron Shield

In this paper we give an analysis of the neutron transmission through an iron sphere using Monte Carlo and transport theory methods based on ENDF/B-VII.1 general purpose library. The motivation for this investigation comes from a well-known deficiency in the iron inelastic data from the older library evaluation (ENDF/B-V), giving a concern for a fast neutron flux underestimation within the reactor pressure vessels. In order to benchmark the next-generation ENDF/B-VI iron data, the U.S. Nuclear Regulatory Commission and the former Czechoslovakian National Research Institute have jointly preformed several experiments in 1990s, addressing neutron leakage spectra obtained for a 252Cf fission source in a centre of an iron sphere. It was shown that the ENDF/B-VI iron cross section, containing several improvements over previous evaluations, will not entirely resolve the neutron spectrum discrepancies observed at high neutron energies. Since safety analyses of reactor pressure vessel embrittlement are often based on neutron transport calculations using specific multigroup cross section libraries, simulation of this benchmark was performed using a hybrid shielding methodology of ADVANTG3.0.3 and MCNP6.1.1b codes. Comparison of calculated and referenced dosimeter activation rates are presented for several "standard" nuclear reactions, often used in reactor pressure vessel dosimetry. For that purpose, the new IRDFF-II special library from the IAEA Nuclear Data Services was used as a reference source of dosimetry cross sections. The MCNP6.1.1b code was used for calculation of reaction rates, which were also compared with previous IRDFF-1.05 special library and general purpose ENDF/B-VII.1 library.