Grand canonical Monte Carlo simulation(GCMCs)is utilized for studying hydrogen storage gravimetric density by pha-graphene at different metal densities,temperatures and pressures.It is demonstrated that the optimum ad...Grand canonical Monte Carlo simulation(GCMCs)is utilized for studying hydrogen storage gravimetric density by pha-graphene at different metal densities,temperatures and pressures.It is demonstrated that the optimum adsorbent location for Li atoms is the center of the seven-membered ring of pha-graphene.The binding energy of Li-decorated phagraphene is larger than the cohesive energy of Li atoms,implying that Li can be distributed on the surface of pha-graphene without forming metal clusters.We fitted the force field parameters of Li and C atoms at different positions and performed GCMCs to study the absorption capacity of H_(2).The capacity of hydrogen storage was studied by the differing density of Li decoration.The maximum hydrogen storage capacity of 4Li-decorated pha-graphene was 15.88 wt%at 77 K and100 bar.The enthalpy values of adsorption at the three densities are in the ideal range of 15 kJ·mol^(-1)-25 kJ·mol^(-1).The GCMC results at different pressures and temperatures show that with the increase in Li decorative density,the hydrogen storage gravimetric ratio of pha-graphene decreases but can reach the 2025 US Department of Energy's standard(5.5 wt%).Therefore,pha-graphene is considered to be a potential hydrogen storage material.展开更多
The adsorption behavior of benzene and propylene in zeolite ZSM-5 was studied by Grand Canonical Monte Carlo（GCMC） simulations. It could be found that benzene and propylene molecules showed different adsorption beha...The adsorption behavior of benzene and propylene in zeolite ZSM-5 was studied by Grand Canonical Monte Carlo（GCMC） simulations. It could be found that benzene and propylene molecules showed different adsorption behavior in the zeolite cavities. The loadings of propylene were significantly larger than those of benzene at 100 kPa. From the figures of potential energy distribution, the potential energy of benzene/zeolite was more negative than that of propylene/zeolite, so benzene could be adsorbed more stably than propylene. When the temperature was in- creased from 298 to 443 K at 100 kPa, the loading ofpropylene was reduced from 99 to 82 molecules, whereas that of benzene changed little. When benzene and propylene were adsorbed in zeolite simultaneously, the competitive adsorption of them occurred; therefore, the potential energy distribution could be changed significantly. Besides, the adsorption isotherms of benzene and propylene in ZSM-5 at 298 and 443 K were simulated. The results exhibit that the different factors influenced the molecular adsorption at various temperatures and pressures, leading to the diffe- rent rules for the adsorption of benzene and propylene molecules in the zeolite. At a low pressure, the unfavorable energy of propylene/zeolite and the ＂commensurate freezing＂ phenomenon of benzene would make the loadings of itself higher than those of propylene. When pressure was higher than 5 kPa, the adsorption of benzene in ZSM-5 would nearly reach saturation.展开更多
The diffusion and adsorption behaviors of benzene and propylene in zeolites MFI, MWW and BEA have been studied by molecular dynamics（MD） and grand canonical Monte Carlo（GCMC） simulations. The diffusion coefficient...The diffusion and adsorption behaviors of benzene and propylene in zeolites MFI, MWW and BEA have been studied by molecular dynamics（MD） and grand canonical Monte Carlo（GCMC） simulations. The diffusion coefficients of benzene and propylene in MFI, MWW and BEA zeolites were calculated by simulating the mean-square displacements（MSD） at 298 and 600 K. Benzene and propylene showed the different adsorption rules in the channels of the three zeolites. For propylene, the molecular loadings decreased in the order： BEA（linear channel）〉BEA （tortuous channel）〉MFI（linear channel）〉MWW（12-membered rings, 12MR channel）〉MFI（tortuous channel）〉MWW （10-membered rings, 10MR channel）; for benzene, the molecular loadings decreased in the order： BEA（linear chan-nel）〉BEA（tortuous channel）〉MWW（12MR channel）〉MFI（linear channel）〉MFI（tortuous channel）〉MWW（10MR channel）. Besides, the adsorption isotherms of benzene and propylene in the three zeolites at 298 and 443 K were simulated. The results show that the different factors influenced the molecular adsorption at various temperatures and pressures, leading to the different rules for the adsorption of benzene and propylene molecules in the zeolites. At a low pressure, the unfavorable energy would make the loadings of propylene lower than those of benzene. When pressure was higher than 0.25 kPa, the adsorption of benzene in MFI would nearly reach saturation.展开更多
Amorphous and crystalline poly （chloro-p-xytylene） （PPX C） membranes are constructed by using a novel com- putational technique, that is, a combined method of NVT＋NPT-molecular dynamics （MD） and gradually reduc...Amorphous and crystalline poly （chloro-p-xytylene） （PPX C） membranes are constructed by using a novel com- putational technique, that is, a combined method of NVT＋NPT-molecular dynamics （MD） and gradually reducing the size （GRS） methods. The related free volumes are defined as homology clusters. Then the sorption and the permeation of gases in PPX C polymers are studied using grand canonical Monte Carlo （GCMC） and NVT-MD methods. The results show that the crystalline PPX C membranes provide smaller free volumes for absorbing or transferring gases relative to the amorphous PPX C area. The gas sorption in PPX C membranes mainly belongs to the physical one, and H bonds can appear obviously in the amorphous area. By cluster analyzing on the mean square displacement of gases, we find that gases walk along the x axis in the crystalline area and walk randomly in the amorphous area. The calculated permeability coefficients are close to the experimental data.展开更多
Grand Canonical Monte Carlo (GCMC) simulations have been performed to study the localization and adsorption behavior of benzene and propylene, in purely siliceous MWW zeolite (ITQ-1). By analyzing the locations of ben...Grand Canonical Monte Carlo (GCMC) simulations have been performed to study the localization and adsorption behavior of benzene and propylene, in purely siliceous MWW zeolite (ITQ-1). By analyzing the locations of benzene and propylene in ITQ-1, it can be deduced that the alkylation of benzene and propylene will mainly happen in 12-MR supercages at the external surface or close to the external surface. The adsorption isotherms of benzene and propylene at 315K and 0 similar to 3.5kPa are predicted, and the results for benzene generally coincide with the trend from the experiments of a series of aromatic compounds.展开更多
The square-well（SW） potential is one of the simplest pair potential models and its phase behavior has been clearly revealed, therefore it has become a benchmark for checking new theories or numerical methods. We int...The square-well（SW） potential is one of the simplest pair potential models and its phase behavior has been clearly revealed, therefore it has become a benchmark for checking new theories or numerical methods. We introduce the generalized canonical ensemble（GCE） into the isobaric replica exchange Monte Carlo（REMC） algorithm to form a novel isobaric GCE-REMC method, and apply it to the study of vapor–liquid transition of SW particles. It is validated that this method can reproduce the vapor–liquid diagram of SW particles by comparing the estimated vapor–liquid binodals and the critical point with those from the literature. The notable advantage of this method is that the unstable vapor–liquid coexisting states,which cannot be detected using conventional sampling techniques, are accessed with a high sampling efficiency. Besides,the isobaric GCE-REMC method can visit all the possible states, including stable, metastable or unstable states during the phase transition over a wide pressure range, providing an effective pathway to understand complex phase transitions during the nucleation or crystallization process in physical or biological systems.展开更多
We consider a network composed of an arbitrary number of directed links. We employ a grand canonical partition function to study the statistical averages of the network in equilibrium. The Hamiltonian is composed of t...We consider a network composed of an arbitrary number of directed links. We employ a grand canonical partition function to study the statistical averages of the network in equilibrium. The Hamiltonian is composed of two parts: a “free” Hamiltonian H0 attributing a constant energy E to each link, and an interacting Hamiltonian Hint involving terms quadratic in the number of links. A Gaussian integration leads to a reformulated Hamiltonian, where now the number of links appears linearly. The reformulated Hamiltonian allows obtaining the exact behavior in limiting cases. At high temperatures the system reproduces the behavior of the free model, while at low temperatures the thermodynamic behavior is obtained by using a renormalized chemical potential, μeff = μ + l, where l is the strength of the interaction. We also resort to a mean field approximation, describing accurately the system over the entire range of all dynamical parameters. A detailed Monte-Carlo simulation verifies our theoretical expectations. We indicate that our model may serve as a prototype model to address a number of different systems.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11904175,11804169,and 11804165)the Graduate Innovation Project of Jiangsu Province,China(Grant No.KYCX210700)。
文摘Grand canonical Monte Carlo simulation(GCMCs)is utilized for studying hydrogen storage gravimetric density by pha-graphene at different metal densities,temperatures and pressures.It is demonstrated that the optimum adsorbent location for Li atoms is the center of the seven-membered ring of pha-graphene.The binding energy of Li-decorated phagraphene is larger than the cohesive energy of Li atoms,implying that Li can be distributed on the surface of pha-graphene without forming metal clusters.We fitted the force field parameters of Li and C atoms at different positions and performed GCMCs to study the absorption capacity of H_(2).The capacity of hydrogen storage was studied by the differing density of Li decoration.The maximum hydrogen storage capacity of 4Li-decorated pha-graphene was 15.88 wt%at 77 K and100 bar.The enthalpy values of adsorption at the three densities are in the ideal range of 15 kJ·mol^(-1)-25 kJ·mol^(-1).The GCMC results at different pressures and temperatures show that with the increase in Li decorative density,the hydrogen storage gravimetric ratio of pha-graphene decreases but can reach the 2025 US Department of Energy's standard(5.5 wt%).Therefore,pha-graphene is considered to be a potential hydrogen storage material.
基金Supported by the National Natural Science Foundation of China(Nos.20576012 and 20625621)
文摘The adsorption behavior of benzene and propylene in zeolite ZSM-5 was studied by Grand Canonical Monte Carlo（GCMC） simulations. It could be found that benzene and propylene molecules showed different adsorption behavior in the zeolite cavities. The loadings of propylene were significantly larger than those of benzene at 100 kPa. From the figures of potential energy distribution, the potential energy of benzene/zeolite was more negative than that of propylene/zeolite, so benzene could be adsorbed more stably than propylene. When the temperature was in- creased from 298 to 443 K at 100 kPa, the loading ofpropylene was reduced from 99 to 82 molecules, whereas that of benzene changed little. When benzene and propylene were adsorbed in zeolite simultaneously, the competitive adsorption of them occurred; therefore, the potential energy distribution could be changed significantly. Besides, the adsorption isotherms of benzene and propylene in ZSM-5 at 298 and 443 K were simulated. The results exhibit that the different factors influenced the molecular adsorption at various temperatures and pressures, leading to the diffe- rent rules for the adsorption of benzene and propylene molecules in the zeolite. At a low pressure, the unfavorable energy of propylene/zeolite and the ＂commensurate freezing＂ phenomenon of benzene would make the loadings of itself higher than those of propylene. When pressure was higher than 5 kPa, the adsorption of benzene in ZSM-5 would nearly reach saturation.
基金Supported by the National Natural Science Foundation of China(No.20576012)the Doctoral Fund of Qingdao University of Science and Technology China(No. 0022430)
文摘The diffusion and adsorption behaviors of benzene and propylene in zeolites MFI, MWW and BEA have been studied by molecular dynamics（MD） and grand canonical Monte Carlo（GCMC） simulations. The diffusion coefficients of benzene and propylene in MFI, MWW and BEA zeolites were calculated by simulating the mean-square displacements（MSD） at 298 and 600 K. Benzene and propylene showed the different adsorption rules in the channels of the three zeolites. For propylene, the molecular loadings decreased in the order： BEA（linear channel）〉BEA （tortuous channel）〉MFI（linear channel）〉MWW（12-membered rings, 12MR channel）〉MFI（tortuous channel）〉MWW （10-membered rings, 10MR channel）; for benzene, the molecular loadings decreased in the order： BEA（linear chan-nel）〉BEA（tortuous channel）〉MWW（12MR channel）〉MFI（linear channel）〉MFI（tortuous channel）〉MWW（10MR channel）. Besides, the adsorption isotherms of benzene and propylene in the three zeolites at 298 and 443 K were simulated. The results show that the different factors influenced the molecular adsorption at various temperatures and pressures, leading to the different rules for the adsorption of benzene and propylene molecules in the zeolites. At a low pressure, the unfavorable energy would make the loadings of propylene lower than those of benzene. When pressure was higher than 0.25 kPa, the adsorption of benzene in MFI would nearly reach saturation.
基金Project supported by the National Natural Science Foundation (Grant No. 11011120241 and 11076002)the China Academy of Engineering Physics "Double Hundred Talents Project" Candidates Optional Subjects (Grant Nos. 2008Rc01 and ZX03010)the China Academy of Engineering Physics Science and Technology Development Fund (Grant No. 2010A0302012)
文摘Amorphous and crystalline poly （chloro-p-xytylene） （PPX C） membranes are constructed by using a novel com- putational technique, that is, a combined method of NVT＋NPT-molecular dynamics （MD） and gradually reducing the size （GRS） methods. The related free volumes are defined as homology clusters. Then the sorption and the permeation of gases in PPX C polymers are studied using grand canonical Monte Carlo （GCMC） and NVT-MD methods. The results show that the crystalline PPX C membranes provide smaller free volumes for absorbing or transferring gases relative to the amorphous PPX C area. The gas sorption in PPX C membranes mainly belongs to the physical one, and H bonds can appear obviously in the amorphous area. By cluster analyzing on the mean square displacement of gases, we find that gases walk along the x axis in the crystalline area and walk randomly in the amorphous area. The calculated permeability coefficients are close to the experimental data.
文摘Grand Canonical Monte Carlo (GCMC) simulations have been performed to study the localization and adsorption behavior of benzene and propylene, in purely siliceous MWW zeolite (ITQ-1). By analyzing the locations of benzene and propylene in ITQ-1, it can be deduced that the alkylation of benzene and propylene will mainly happen in 12-MR supercages at the external surface or close to the external surface. The adsorption isotherms of benzene and propylene at 315K and 0 similar to 3.5kPa are predicted, and the results for benzene generally coincide with the trend from the experiments of a series of aromatic compounds.
基金supported by the National Natural Science Foundation for Outstanding Young Scholars,China(Grant No.11422542)the National Natural Science Foundation of China(Grant Nos.11605151 and 11675138)the Shanghai Supercomputer Center of China and Special Program for Applied Research on Super Computation of the NSFC–Guangdong Joint Fund(the second phase)
文摘The square-well（SW） potential is one of the simplest pair potential models and its phase behavior has been clearly revealed, therefore it has become a benchmark for checking new theories or numerical methods. We introduce the generalized canonical ensemble（GCE） into the isobaric replica exchange Monte Carlo（REMC） algorithm to form a novel isobaric GCE-REMC method, and apply it to the study of vapor–liquid transition of SW particles. It is validated that this method can reproduce the vapor–liquid diagram of SW particles by comparing the estimated vapor–liquid binodals and the critical point with those from the literature. The notable advantage of this method is that the unstable vapor–liquid coexisting states,which cannot be detected using conventional sampling techniques, are accessed with a high sampling efficiency. Besides,the isobaric GCE-REMC method can visit all the possible states, including stable, metastable or unstable states during the phase transition over a wide pressure range, providing an effective pathway to understand complex phase transitions during the nucleation or crystallization process in physical or biological systems.
文摘We consider a network composed of an arbitrary number of directed links. We employ a grand canonical partition function to study the statistical averages of the network in equilibrium. The Hamiltonian is composed of two parts: a “free” Hamiltonian H0 attributing a constant energy E to each link, and an interacting Hamiltonian Hint involving terms quadratic in the number of links. A Gaussian integration leads to a reformulated Hamiltonian, where now the number of links appears linearly. The reformulated Hamiltonian allows obtaining the exact behavior in limiting cases. At high temperatures the system reproduces the behavior of the free model, while at low temperatures the thermodynamic behavior is obtained by using a renormalized chemical potential, μeff = μ + l, where l is the strength of the interaction. We also resort to a mean field approximation, describing accurately the system over the entire range of all dynamical parameters. A detailed Monte-Carlo simulation verifies our theoretical expectations. We indicate that our model may serve as a prototype model to address a number of different systems.
