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Bug in 4.2.0 checkpointing code
From: |
Jean-Noël Grad |
Subject: |
Bug in 4.2.0 checkpointing code |
Date: |
Sat, 24 Dec 2022 00:28:03 +0100 |
User-agent: |
Roundcube Webmail/1.4.13 |
Dear ESPResSo users,
It has come to our attention that the checkpointing mechanism was broken
in release 4.2.0. When reloading the state of the system from a
checkpoint file, if the DIPOLES feature is part of the myconfig file,
the magnetic dipole moment overwrites the particle director, which
causes non-magnetic particles to be all aligned along the z-axis. This
bug breaks momentum conservation and can lead to nonphysical forces
being applied in simulations where the particle director plays a role
(ex: relative virtual sites, Gay-Berne potential, anisotropic particles,
active particles, etc.). Since the default myconfig file contains
DIPOLES, most ESPResSo users are affected. In addition, when reloading
from a checkpoint file, the particle angular velocity in the body frame
is sometimes calculated using a default-constructed quaternion instead
of the particle quaternion.
These issues have been fixed in the python branch of ESPResSo (PR #4637)
and will be fixed in the upcoming 4.2.1 bugfix release (PR #4611).
If you are using 4.2.0 and need checkpointing for simulations with the
ROTATION feature, you can update ESPResSo 4.2.0 locally with the
following git commands:
```sh
git remote add upstream https://github.com/espressomd/espresso.git
git fetch upstream pull/4611/head:pr-4611
git cherry-pick 992f093ce947b
```
We are sorry for the inconvenience.
Best regards,
Jean-Noël Grad
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