Modeling the High-Pressure Solid and Liquid Phases of Tin from Deep Potentials with ab initio Accuracy

Constructing an accurate atomistic model for the high-pressure phases of tin (Sn) is challenging because properties of Sn are sensitive to pressures. We develop machine-learning-based deep potentials for Sn with pressures ranging from 0 to 50 GPa and temperatures ranging from 0 to 2000 K. In particular, we find the deep potential, which is obtained by training the ab initio data from density functional theory calculations with the state-of-the-art SCAN exchange-correlation functional, is suitable to characterize high-pressure phases of Sn. We systematically validate several structural and elastic properties of the {\alpha} (diamond structure), {\beta}, bct, and bcc structures of Sn, as well as the structural and dynamic properties of liquid Sn. The thermodynamics integration method is further utilized to compute the free energies of the {\alpha}, {\beta}, bct, and liquid phases, from which the deep potential successfully predicts the phase diagram of Sn including the existence of the triple-point that qualitatively agrees with the experiment

A Spin-dependent Machine Learning Framework for Transition Metal Oxide Battery Cathode Materials

Owing to the trade-off between the accuracy and efficiency, machine-learning-potentials (MLPs) have been widely applied in the battery materials science, enabling atomic-level dynamics description for various critical processes. However, the challenge arises when dealing with complex transition metal (TM) oxide cathode materials, as multiple possibilities of d-orbital electrons localization often lead to convergence to different spin states (or equivalently local minimums with respect to the spin configurations) after ab initio self-consistent-field calculations, which causes a significant obstacle for training MLPs of cathode materials. In this work, we introduce a solution by incorporating an additional feature - atomic spins - into the descriptor, based on the pristine deep potential (DP) model, to address the above issue by distinguishing different spin states of TM ions. We demonstrate that our proposed scheme provides accurate descriptions for the potential energies of a variety of representative cathode materials, including the traditional Li$_x$TMO$_2$ (TM=Ni, Co, Mn, $x$=0.5 and 1.0), Li-Ni anti-sites in Li$_x$NiO$_2$ ($x$=0.5 and 1.0), cobalt-free high-nickel Li$_x$Ni$_{1.5}$Mn$_{0.5}$O$_4$ ($x$=1.5 and 0.5), and even a ternary cathode material Li$_x$Ni$_{1/3}$Co$_{1/3}$Mn$_{1/3}$O$_2$ ($x$=1.0 and 0.67). We highlight that our approach allows the utilization of all ab initio results as a training dataset, regardless of the system being in a spin ground state or not. Overall, our proposed approach paves the way for efficiently training MLPs for complex TM oxide cathode materials

Catalytic Hydrogen Evolution of NaBH4_4 Hydrolysis by Cobalt Nanoparticles Supported on Bagasse-Derived Porous Carbon

As a promising hydrogen storage material, sodium borohydride (NaBH4) exhibits superior stability in alkaline solutions and delivers 10.8 wt.% theoretical hydrogen storage capacity. Nevertheless, its hydrolysis reaction at room temperature must be activated and accelerated by adding an effective catalyst. In this study, we synthesize Co nanoparticles supported on bagasse-derived porous carbon (Co@xPC) for catalytic hydrolytic dehydrogenation of NaBH$_4$. According to the experimental results, Co nanoparticles with uniform particle size and high dispersion are successfully supported on porous carbon to achieve a Co@150PC catalyst. It exhibits particularly high activity of hydrogen generation with the optimal hydrogen production rate of 11086.4 mL$_{H2}$∙min$^{H2}$∙g$_{Co}$$^{H2}$ and low activation energy (E$_{a}$) of 31.25 kJ mol$^{H2}$. The calculation results based on density functional theory (DFT) indicate that the Co@xPC structure is conducive to the dissociation of [BH$_{4}$]$^{-}$, which effectively enhances the hydrolysis efficiency of NaBH$_4$. Moreover, Co@150PC presents an excellent durability, retaining 72.0% of the initial catalyst activity after 15 cycling tests. Moreover, we also explored the degradation mechanism of catalyst performance

Dielectric properties of pyridine derivative-water clusters: Molecular dynamics simulation

We analyzed the dielectric properties of pyridine derivative-water clusters using the external field method with reaction field approximations. The average dipole moment along the direction of applied field, (M), linearly increases with certain field strengths. The reinterpretation of the Kirkwood factor Gk and A associated with the static electric field is imperative. The external field method is more accurate for molecular liquids with dipole moments whereas the fluctuation method yields better performance for molecules with large permanent dipole moments. Finally, we find that the static electric field can prolong lifetimes of hydrogen bonds and increase the average hydrogen-bond number. (C) 2017 Elsevier B.V. All rights reserved

Mobile data collection method used in PMS

Paper presented at the 24th Annual Southern African Transport Conference 11 - 13 July 2005 "Transport challenges for 2010", CSIR International Convention Centre, Pretoria, South Africa.This paper was transferred from the original CD ROM created for this conference. The material on the CD ROM was published using Adobe Acrobat technology. The original CD ROM was produced by Document Transformation Technologies Postal Address: PO Box 560 Irene 0062 South Africa. Tel.: +27 12 667 2074 Fax: +27 12 667 2766 E-mail: [email protected] URL: http://www.doctech.co.z

The Influence of Sodium Iodide Salt on the Interfacial Properties of Aqueous Methanol Solution by a Combined Molecular Simulation and Sum Frequency Generation Vibrational Spectroscopy Study

Understanding the influence of salt ions on the microscopic properties of liquid interfaces is of both fundamental and practical importance. A large number of previous experimental and theoretical investigations have explored the salt effects on the surfaces of either pure water or neat organic liquid. However, how the salt ions affect the interfacial structures of water/organic liquid mixtures has rarely been studied. Here, the molecular dynamics (MD) simulations and sum frequency generation vibrational spectroscopy (SFG-VS) were carried out to investigate the influence of sodium iodide (NaI) on the air/liquid interfaces of the methanol-water mixtures. The SFG-VS spectral intensities were discovered to increase with the addition of 3 M NgI while the center frequencies of the C-H stretching vibrations at high methanol concentrations showed a similar to 2 cm(-1) blue shift compared with those obtained before adding NaI. The MD results indicated that Na+ and I- can only affect Part I (near the bulk phase) but not Part II (near the gas phase) of the interfacial region. It was also found that the average orientations of interfacial methyl groups were constant and not effectively disturbed by the changes of methanol concentrations or the addition of NaI. It is therefore concluded that the changes of the SFG-VS intensities upon the addition of NaI salts were mainly caused by the increasing number of interfacial methanol molecules. Further analysis showed that the existence of NaI affects the surface tensions more for the interfaces with higher bulk methanol concentrations, which is in agreement with the SFG-VS results. It is noteworthy that the maximum number density of methanol molecules with the net nonzero orientations is reached near the Gibbs dividing surface, the reasons of which are worth further investigating

An epidemiological study of etiology and clinical characteristics in patients with nontraumatic osteonecrosis of the femoral head

Background: Osteonecrosis of the femoral head (ONFH) is a common disease with high disability rate. However, a few studies investigate the etiology and clinical characteristics of nontraumatic ONFH patients in China. Therefore, we conducted this cross-sectional study. Materials and Methods: Totally, information of 7268 nontraumatic ONFH patients treated between August 2005 and August 2015 was extracted from the medical records. The extracted information included the age, gender, diagnostic criteria, cause of nontraumatic ONFH, types of steroid use, and types of alcohol. Results: Among these included patients, there were 5126 (70.5%) male patients with average age of 44.5 years and 2142 (29.5%) female patients with average age of 47.6 years (P = 0.54). The number of steroid-, alcohol-, steroid/alcohol-, and idiopathic-induced nontraumatic ONFH men patients was 1684, 2310, 364, and 768, respectively, and nontraumatic ONFH women patients was 1058, 482, 140, and 462, respectively. Meanwhile, we found that both the levels of triglycerides (P = 0.03) and low-density lipoprotein (P = 0.02) were significantly changed in the idiopathic-induced nontraumatic ONFH patients. Conclusion: These results indicated the earlier onset of nontraumatic ONFH in male patients than in female patients, different main etiology for male (alcohol consumption) and female (steroid use) patients, and close relationship between the lipid metabolism and idiopathic-induced nontraumatic ONFH. Our findings could be helpful for researchers to investigate the pathogenesis of ONFH and aid the clinicians in the early prevention and diagnosis of nontraumatic ONFH