Allow triclinic boxes in MPCD #1950
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This should be merged after PR #1951. |
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@joaander I finished my benchmarks for this PR, and they are acceptable to me. We have also run pretty long simulations with various skewed boxes on a single GPU without observing any errors. So, I think this PR is ready to be merged. |
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Description
This PR generalizes the MPCD cell list code to allow triclinic simulation boxes. The cells are aligned to the lattice vectors rather than being a simple cubic lattice. This means that the MPCD cells can be skewed by a tilt factor as well as orthorhombic non-cubic.
Benchmark
SRD solvent with density 10, collision angle 130, and kT = 1 in cube with L = 120.
CPU: 2x Intel Xeon Gold 6248R = 48 cores (Auburn University Easley)
GPU: 1x A100 (NCSA Delta GPU)
No change on GPU (A100 is compute hungry), and only a small penalty on CPU. This performance is acceptable to me in order to enable more flexibility.
Motivation and context
This generalization of the code is necessary to enable simulation methods that deform the box, e.g., Lees-Edwards shear flow implemented using the Lagrangian rhomboid method. It also puts less restrictions on the user to make their cells exactly cubic.
Resolves #773
How has this been tested?
Existing C++ tests of the cell list have been generalized to triclinic boxes. There were some cases that no longer worked as originally written because of floating-point rounding. I am also planning a subsequent PR that will change the way MPCD does domain decomposition so that there will be no cells crossing boundaries anymore. Hence, these cases should become irrelevant.
Checklist:
sphinx-doc/credits.rst) in the pull request source branch.CHANGELOG.rstfollowing the established format.