Hoang Anh (Benjamin) Nguyen

Hoang Anh (Benjamin) Nguyen

Physical Scientist

Publications

Crystallization of Liquid Silica under Compression: A Molecular Dynamics Simulation Permalink

Published in Pramana - Journal of Physics, 2024

In this study, we employ molecular dynamics simulations to develop a large model (19,998 atoms) of liquid SiO2 at 3500 K. We construct models at different pressures in the 0-100 GPa range using the BKS potential and periodic boundary conditions. The goal is to detail the structural transition from the polyamorphic liquid state of SiO2 to the crystalline stishovite form, which occurs between 45 and 60 GPa. We analyze the polyamorphic state of liquid SiO2 by examining the formation of SiOx clusters from 2 GPa to 60 GPa. Beyond 60 GPa, the Pair Radial Distribution Functions (PRDFs) for Si-O, O-O, and Si-Si display multiple peaks, indicating the crystalline phase. This observation is further supported by examining the bond angle distribution, the fraction of SiOx units and OSix linkages, Si-O bond lengths within SiOx units, structural visualizations, and the analysis of ring statistics in the liquid SiO2 system, all of which underscore the comprehensive changes in the system’s structure. Read more

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Computer simulation of phosphate-silicate and calcium phosphate-silicate systems Permalink

Published in Physica Scripta, 2023

The structure of P2O5-SiO2 and CaO-P2O5-SiO2 systems have been systematically investigated by molecular dynamics simulation. The structural characteristics were clarified with intuitive figures and images at atomic scale. Specially, we have applied the recognition and visualization methods to clarify short-range order, intermediate-range order, and network structure. The structural and compositional heterogeneities and mechanisms of alkaline Earth metals incorporation into -O-P-O-Si-O- network have been discussed in detail. This is useful information for designing bioactive systems with many potential applications. Read more

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Study of the structure of MgSiO3 system under compression by using ring statistics and voronoi analysis Permalink

Published in Physica Scripta, 2023

The structural change of MgSiO3 liquid under compression is still one of the most interesting challenges. In this paper, we perform molecular dynamics simulations to study the structural change of MgSiO3 liquid from 0 to 200 GPa. Ring statistics are analyzed to clarify the intermediate-range order, to explain why the second peak of Si–Si PRDFs splits into two subpeaks at 200 GPa, and to show the heterogeneity of MgSiO3. Large rings, which form at high pressures, capture the oxygen atoms. Oxygen atoms, which have a negative charge, attract Mg²⁺ ions, creating magnesium-rich regions. Additionally, the Voronoi and Qn distribution changes on the ring with pressure are clarified to provide more information about the rings. Read more

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Pressure-induced Glassy Networks of Enstatite (MgSiO3) and Forsterite (Mg2SiO4) Permalink

Published in VNU Journal of Science: Mathematics - Physics, 2023

This work is designed to focus on the glassy network analysis and visualizing the cluster and subnets formation, the rich set of bond-, edge-, and face-sharing linkages. The correlation between the degree of polymerization and linkages forming is apparently indicated. The distribution of SiOx clusters is computed to determine the polymerization characteristic and Mg-rich region. The distribution of BOs, NBOs, and FOs also are investigated to prove the behavior of Mg2+ incorporating into the -Si-O- network. Polyhedral units, clusters, and subnets are vividly visualized so as to have a better understanding of cluster merging. Besides, in this work, we have also clarified the distribution of edge-sharing and face-sharing subnets/network between Si-Si and Mg-Si species. Read more

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Some results of seismic travel-time reflection tomography study Permalink

Published in Petro Vietnam, 2021

Velocity model is essential for seismic data processing as it plays an important role in migration processes as well as time depth conversion. There are several techniques to reach that goal, among which tomographic inversion is an efficient one. As an upgrade version of handpicked velocity analysis, the tomography technique is based on the reflection ray tracing and conjugate gradient method to estimate an optimum velocity model and can create an initial high quality model for other intensive imaging and modelling module such as reverse-time migration (RTM) and full-waveform inversion (FWI). For the mentioned benefit, we develop a seismic travel-time reflection tomography (SeisT) module to study the accuracy of the approach along with building the technical capability in seismic processing. The accuracy of the module has been tested by both synthetic and real seismic field data; the efficiency and the accuracy of the model have been proven in terms of development method as well as field data application. Read more

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Structural Simulation of Mg2SiO4 under Compression Permalink

Published in VNU Journal of Science: Mathematics - Physics, 2020

The microstructure in Mg2SiO4 glass under high compression is studied by molecular dynamics method. This work revealed the correlation between pair radial distribution functions (PRDF) of Si-Si pair and bond angle distribution (BAD) of Si-O-Si and focuses on clarifying the split peak of Si-Si PRDF. Moreover, visualizing the bonds of Si-Si at different pressures shows the changing of Si-Si bonds with pressure. In particular, as pressure increases, it forms corner-sharing, edge-sharing, and face-sharing bonds between SiOx coordination units, resulting in the first peak splitting of Si-Si PRDF at high pressure. The results of Si-Si’s PRDF have also been analyzed and explained in detail. Read more

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Topology of SiOx-units and glassy network of magnesium silicate glass under densification: correlation between radial distribution function and bond angle distribution Permalink

Published in Modelling and Simulation in Materials Science and Engineering, 2020

Topology of SiOx units and glassy network of magnesium silicate glass at different pressures are investigated by molecular dynamics simulation to clarify its microstructure under compression. Results show that SiOx-topology and glassy network structure are significantly dependent on pressure. At ambient pressure, the –Si–O– glassy network in Mg2SiO4 glass is split into subnets/clusters. Under compression, the small subnets tend to merge each other forming larger ones. The decrease of Si–O–Si bond angle under compression that accompanies a formation of edge- and face-sharing bonds between SiOx units results in the first peak splitting of Si–Si PRDF at high pressure. In particular, the investigation also reveals a tight correlation between PRDFs (Si–Si, Mg–Mg, Si–Mg, O–O) and BADs (Si–O–Si, Mg–O–Mg, Mg–O–Si, O–T–O (T = Si, Mg)), respectively. The spatial distribution of corner-, edge- and face-sharing bonds is not uniform but forming subnets/clusters. The clusters of face-sharing bonds form rigid particles embedding into mixture clusters of corner- and edge-sharing bonds. Size distribution of subnets/clusters (SiOx-cluster as well as clusters of corner-, edge- and face-sharing bonds) under compression also has been investigated to clarify the intermediate range order. The characteristic change of PRDFs under compression in the relationship with microstructural change and the mechanism of magnesium ions incorporation into –Si–O– network is also discussed in detail. Read more

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