38 lines
1.4 KiB
Plaintext
38 lines
1.4 KiB
Plaintext
This directory shows how to use the `fix born` command
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to calculate the full matrix of elastic constants
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for cubic diamond at finite temperature
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running the Stillinger-Weber potential.
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The input script `in.elastic` can be run
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directly from LAMMPS, or via a Python wrapper
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script.
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to run directly from LAMMPS, use:
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mpirun -np 4 lmp.exe -in in.elastic
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This simulates an orthorhombic box with the cubic crystal axes
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aligned with x, y, and z.
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The default settings replicate the 1477~K benchmark of
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Kluge, Ray, and Rahman (1986) that is Ref.[15] in:
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Y. Zhen, C. Chu, Computer Physics Communications 183(2012) 261-265
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The script contains many adjustable parameters that can be used
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to generate different crystal structures, supercell sizes,
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and sampling rates.
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to run via the Python wrapper, use:
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mpirun -np 4 python elastic.py
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This will first run the orthorhombic supercell as before,
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follows by an equivalent simulation using a triclinic structure.
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The script shows how the standard triclinic primitive cell for cubic diamond
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can be rotated in to the LAMMPS upper triangular frame. The resultant
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elastic constant matrix does not exhibit the standard symmetries of cubic crystals.
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However, the matrix is then rotated back to the standard orientation
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to recover the cubic symmetry form of the elastic matrix,
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resulting in elastic constants that are the same for both
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simulations, modulo statistical uncertainty.
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