Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

In this paper, deformation behaviors and microstructure evolution of a hot-rolled AZ31B magnesium alloy under cyclic loadings are investigated. The relationship between plastic deformation and microstructure evolution and the crack formation mechanisms are discussed. Under a high cyclic stress (90–140 MPa), steady ratcheting effect occurred in the material and the development of ratcheting strain went through three stages: 1) Stage I - initial rapid increase stage; 2) Stage II - steady stage; and 3) Stage III - final abrupt increase stage. Under a low cyclic stress (≤ 90 MPa), inconspicuous ratcheting effect was found in the material, indicating a light damage in the material. When the cyclic stress is below 30 MPa, no ratcheting effect is found and only elastic deformation occurs in the material. The formation of cracks in Stages I & II is mainly due to the activation of the basal slip system. The mean geometrically necessary dislocations (GND) are calculated to analyze the relationship between the basal slip and the ratcheting effect during the cyclic loading. Finally, a new approach is proposed to estimate the AZ31B magnesium alloy’s cyclic strength (at 107 cycles) according to the cyclic stress at which steady ratcheting effect starts to occur in the material.

Deformation behaviors and cyclic strength assessment of AZ31B magnesium alloy based on steady ratcheting effect

Disconnections and other defects associated with twin interfaces

Effect of local stress fields on twin characteristics in HCP metals

[Zhang, Z. J.; Zhang, P.; Li, L. L.; Zhang, Z. F.] Chinese Acad Sci, Shenyang Natl Lab Mat Sci, Inst Met Res, Shenyang 110016, Peoples R China.;Zhang, ZF (reprint author), Chinese Acad Sci, Shenyang Natl Lab Mat Sci, Inst Met Res, 72 Wenhua Rd, Shenyang 110016, Peoples R China.;zhfzhang@imr.ac.cn

Fatigue cracking at twin boundaries: Effects of crystallographic orientation and stacking fault energy (vol 60, pg 3113, 2012)

Observations on the intersection between 101̅2 twin variants sharing the same zone axis in deformed magnesium alloy

https://par.nsf.gov/servlets/purl/10059819

Non-dislocation-mediated basal stacking faults inside 101−1 twins

Using transmission electron microscopy, we characterised the structures of the boundary caused by the interactions between different twin variants that share the same zone axis in a deformed magnes...

Li Tan

Papers

Observations on the intersection between 101̅2 twin variants sharing the same zone axis in deformed magnesium alloy

Non-dislocation-mediated basal stacking faults inside 101−1 twins

Investigation of twin–twin interaction in deformed magnesium alloy

Structural characterization of {101¯3} twin boundaries in deformed cobalt

Two types of basal stacking faults within { 10 1 2 } twin in deformed magnesium alloy