scholarly journals Speed-Dependent Adaptive Partitioning QM/MM for Displacement Damage Simulations

2020 ◽  
Author(s):  
Zenghui Yang
Keyword(s):  
Active Region ◽  
Ab Initio ◽  
Rapid Change ◽  
Active Regions ◽  
Chem Phys ◽  
Model Systems ◽  
Harsh Environments ◽  
Adaptive Partitioning ◽  
Energy Conserving ◽  
Dependent Potential

Solids receive displacement damages (DD) when interacting with energetic particles, which may happen during the fabrication of semiconductor devices, in harsh environments and in certain analysis techniques. Simulations of the DD generation are usually carried out with classical molecular dynamics (MD), but classical MD does not account for all the effects in DD, as demonstrated by <i>ab initio</i> calculations of model systems in literature. A fully <i>ab initio</i> simulation of the DD generation is impractical due to the large number of atoms involved. In my previous paper [Phys. Chem. Chem. Phys. 22, 19307 (2020)], I developed an adaptive-center (AC) method for adaptive-partitioning (AP) quantum mechanics/molecular mechanics (QM/MM) simulations, allowing the active region centers and the QM/MM partition to be determined on-the-fly for energy-conserving AP-QM/MM methods. I demonstrated that the AC-AP-QM/MM is applicable to the simulation of the DD generation, so that the active regions can be treated with an <i>ab initio</i> method. The AC method was unable to identify the fast-moving recoil ions in the DD generation as active region centers, however, and the accuracy is negatively affected by the rapid change in QM/MM partition of the system. In this paper, I extend the AC method and develop a speed-dependent adaptive-center (SDAC) method for proper AP-QM/MM simulations of DD. The SDAC method is applicable to general problems with speed-dependent active regions, and is compatible with all existing energy-conserving partition-by-distance AP-QM/MM methods. The artifact due to the speed-dependent potential energy surface can be made small by choosing proper criteria. I demonstrate the SDAC method by simulations of the DD generation in bulk Silicon.<br>

scholarly journals Speed-Dependent Adaptive Partitioning QM/MM for Displacement Damage Simulations

2020 ◽  
Author(s):  
Zenghui Yang
Keyword(s):  
Active Region ◽  
Ab Initio ◽  
Rapid Change ◽  
Active Regions ◽  
Chem Phys ◽  
Model Systems ◽  
Harsh Environments ◽  
Adaptive Partitioning ◽  
Energy Conserving ◽  
Dependent Potential

Solids receive displacement damages (DD) when interacting with energetic particles, which may happen during the fabrication of semiconductor devices, in harsh environments and in certain analysis techniques. Simulations of the DD generation are usually carried out with classical molecular dynamics (MD), but classical MD does not account for all the effects in DD, as demonstrated by <i>ab initio</i> calculations of model systems in literature. A fully <i>ab initio</i> simulation of the DD generation is impractical due to the large number of atoms involved. In my previous paper [Phys. Chem. Chem. Phys. 22, 19307 (2020)], I developed an adaptive-center (AC) method for adaptive-partitioning (AP) quantum mechanics/molecular mechanics (QM/MM) simulations, allowing the active region centers and the QM/MM partition to be determined on-the-fly for energy-conserving AP-QM/MM methods. I demonstrated that the AC-AP-QM/MM is applicable to the simulation of the DD generation, so that the active regions can be treated with an <i>ab initio</i> method. The AC method was unable to identify the fast-moving recoil ions in the DD generation as active region centers, however, and the accuracy is negatively affected by the rapid change in QM/MM partition of the system. In this paper, I extend the AC method and develop a speed-dependent adaptive-center (SDAC) method for proper AP-QM/MM simulations of DD. The SDAC method is applicable to general problems with speed-dependent active regions, and is compatible with all existing energy-conserving partition-by-distance AP-QM/MM methods. The artifact due to the speed-dependent potential energy surface can be made small by choosing proper criteria. I demonstrate the SDAC method by simulations of the DD generation in bulk Silicon.<br>

On-the-Fly Determination of Active Region Centers in Adaptive-Partitioning QM/MM

2020 ◽  
Author(s):  
Zenghui Yang
Keyword(s):  
Quantum Mechanics ◽  
Active Region ◽  
Molecular Mechanics ◽  
Active Regions ◽  
Available Energy ◽  
Adaptive Partitioning ◽  
Different Levels

Quantum mechanics/molecular mechanics (QM/MM) methods partition the system into active and environmental regions and treat them with different levels of theory, achieving accuracy and efficiency at the same time. Adaptive-partitioning (AP) QM/MM methods allow on-the-fly changes to the QM/MM partitioning of the system. Many of the available energy-based AP-QM/MM methods partition the system according to distances to pre-chosen centers of active regions. For such AP-QM/MM methods, I develop an adaptive-center (AC) method that allows on-the-fly determination of the centers of active regions according to general geometrical or potential-related criteria, extending the range of application of energy-based AP-QM/MM methods to systems where active regions may occur or vanish during the simulation.

scholarly journals On-the-Fly Determination of Active Region Centers in Adaptive-Partitioning QM/MM

2020 ◽  
Author(s):  
Zenghui Yang
Keyword(s):  
Quantum Mechanics ◽  
Active Region ◽  
Molecular Mechanics ◽  
Active Regions ◽  
Available Energy ◽  
Adaptive Partitioning ◽  
Different Levels

Quantum mechanics/molecular mechanics (QM/MM) methods partition the system into active and environmental regions and treat them with different levels of theory, achieving accuracy and efficiency at the same time. Adaptive-partitioning (AP) QM/MM methods allow on-the-fly changes to the QM/MM partitioning of the system. Many of the available energy-based AP-QM/MM methods partition the system according to distances to pre-chosen centers of active regions. For such AP-QM/MM methods, I develop an adaptive-center (AC) method that allows on-the-fly determination of the centers of active regions according to general geometrical or potential-related criteria, extending the range of application of energy-based AP-QM/MM methods to systems where active regions may occur or vanish during the simulation.

scholarly journals Sensitivity of low-degree solar p modes to active and ephemeral regions: frequency shifts back to the Maunder minimum

2019 ◽  
Vol 489 (1) ◽  
pp. L86-L90 ◽  
Author(s):  
William J Chaplin ◽  
Rachel Howe ◽  
Sarbani Basu ◽  
Yvonne Elsworth ◽  
Timothy W Milbourne ◽  
...  
Keyword(s):  
Active Region ◽  
Magnetic Fields ◽  
Spatial Scales ◽  
Active Regions ◽  
Activity Cycle ◽  
Maunder Minimum ◽  
Field Frequency ◽  
Frequency Shifts ◽  
Near Surface ◽  
Low Degree

ABSTRACT We explore the sensitivity of the frequencies of low-degree solar p modes to near-surface magnetic flux on different spatial scales and strengths, specifically to active regions with strong magnetic fields and ephemeral regions with weak magnetic fields. We also use model reconstructions from the literature to calculate average frequency offsets back to the end of the Maunder minimum. We find that the p-mode frequencies are at least 3 times less sensitive (at 95  per cent confidence) to the ephemeral-region field than they are to the active-region field. Frequency shifts between activity cycle minima and maxima are controlled predominantly by the change of active region flux. Frequency shifts at cycle minima (with respect to a magnetically quiet Sun) are determined largely by the ephemeral flux, and are estimated to have been $0.1\, \rm \mu Hz$ or less over the last few minima. We conclude that at epochs of cycle minimum, frequency shifts due to near-surface magnetic activity are negligible compared to the offsets between observed and model frequencies that arise from inaccurate modelling of the near-surface layers (the so-called surface term). The implication is that this will be the case for other Sun-like stars with similar activity, which has implications for asteroseismic modelling of stars.

scholarly journals Correction: Penetrating probability and cross section of the Li+–C60 encapsulation process through an ab initio molecular dynamics investigation

2018 ◽  
Vol 20 (41) ◽  
pp. 26786-26786
Author(s):  
Thi H. Ho ◽  
Yoshiyuki Kawazoe ◽  
Hung M. Le
Keyword(s):  
Molecular Dynamics ◽  
Ab Initio ◽  
Cross Section ◽  
Chem Phys ◽  
Ab Initio Molecular Dynamics ◽  
Encapsulation Process ◽  
Phys Chem Chem Phys

Correction for ‘Penetrating probability and cross section of the Li+–C60 encapsulation process through an ab initio molecular dynamics investigation’ by Thi H. Ho et al., Phys. Chem. Chem. Phys., 2018, 20, 7007–7013.

scholarly journals Statistical Properties of Magnetic Separators in Model Active Regions

2000 ◽  
Vol 195 ◽  
pp. 443-444
Author(s):  
B. T. Welsch ◽  
D. W. Longcope
Keyword(s):  
Active Region ◽  
Solar Corona ◽  
Magnetic Reconnection ◽  
First Principles ◽  
Magnetic Charge ◽  
Active Regions ◽  
Heating Rates ◽  
X Ray ◽  
Field Lines ◽  
Charge Topology

“Transient brightenings” (or “microflares”) regularly deposit 1027 ergs of energy in the solar corona, and account for perhaps 20% of the active corona's power (Shimizu 1995). We assume these events correspond to episodes of magnetic reconnection along magnetic separators in the solar corona. Using the techniques of magnetic charge topology, we model active region fields as arising from normally distributed collections of “magnetic charges”, point-like sources/sinks of flux (or field lines). Here, we present statistically determined separator (X-ray loop) lengths, derived from first principles. We are in the process of statistical calculations of heating rates due to reconnection events along many separators.

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