|Gromacs| 2018.3 release notes
------------------------------

This version was released on August 23, 2018. These release notes document
the changes that have taken place in |Gromacs| since version 2018.2, to fix known
issues. It also incorporates all fixes made in version 2016.5 and
earlier, which you can find described in the :ref:`release-notes`.

Fixes where mdrun could behave incorrectly
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Multi-domain GPU runs can no longer miss pair interactions
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

With systems with empty space in the unit cell, GPU runs with domain
decomposition would not compute LJ and Coulomb interactions between
domains when there we no interactions between domains on a rank at some
point in time.

 - This bug only affects simulations running on GPUs with domain decomposition
   and containing empty regions of space that can lead to domains being empty.
 - Possible observations of this bug may have been seemingly random failures
   of calculations that where not reproducible when restarting a simulation
   from a checkpoint file, as the domain would then again be filled properly
   if interactions are present at the beginning.
 - It is unlikely that this bug will have unnoticed effects on all but
   very short simulations, as the missing interactions will inevitable lead
   to simulation instability and crashes.
 - If a simulation that crashed due to this bug is restarted it can contain
   a small region around the crash that will be unphysical due to some
   interactions not being calculated just before the crash itself.

**This is a critical fix and users of 2018.x series that run on GPUs should
update to this point release**

:issue:`2502`

Fix Conjugate Gradient assertion failure at end of minimization
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

When the final step coincided with a coordinate output step,
conjugate gradient minimization would exit with an assertion failure
instead of writing confout.gro.

:issue:`2554`

Multi-domain Conjugate Gradient minimimization no longer segfaults.
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

:issue:`2554`

Fix pairlist buffer with Brownian Dynamics
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

With Brownian Dynamics and bd-fric > 0, the Verlet pairlist buffer would
be determined with incorrect masses for constrained atoms and virtual
sites. This would lead to a too small buffer for typical atomistic
systems with constraints.

:issue:`2613`

Avoid "atom moved to far" errors
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

The introduction of the dual pair list has led to larger nstlist values,
which leads to larger atom displacements between domain decomposition
steps. This has made it more likely that the errors
"An atom moved too far between two domain decomposition steps" and
"N particles communicated to PME rank M are more than 2/3 times the cut-off
out of the domain decomposition cell ..." appear for stable systems.
Now atom displacements are correctly taken into account when determining
the minimum cell size, so these errors should only appear for unstable systems.

:issue:`2614`

grompp now checks that pull groups are not close to half the box size
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

Pull groups that use a reference atom for periodic boundary treatment
should have all their atoms well within half the box size of this reference.
When this is not the case, grompp will issue a warning.

:issue:`2397`

Fixed segmentation fault in mdrun with QM/MM ONIOM scheme
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

:issue:`2617`

Correctly specified that PME on GPUs is only supported for dynamical integrators
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

Previously PME on GPU support could run (but fail) for energy
minimization and normal-mode analysis runs.

:issue:`2578`

Fixes for ``gmx`` tools
^^^^^^^^^^^^^^^^^^^^^^^

Fixed syntax error in make_gromos_rtp.py
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

:issue:`2557`

Fix gmx solvate topology updating
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

Removed hard coded solvent names to allow updates to topology based on
solvent molecule information. Also allows updating with multiple solvent
types.

:issue:`1929`

Fix bfactor output error caused by fix for :issue:`2511`
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
The fix for the PQR file output broke the output of bfactors from other tools.

:issue:`2575`

Made sure that gmx rms can skip values
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
When requested to skip values, gmx rms would still output all values despite
the option. Now it only outputs values that are requested to be processed.

:issue:`2565`

Fix trjconv when not providing structure file
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

trjconv would fail with a segmentation violation when running without any structure
file due to incomplete initialization of the topology data structure. This fix adds
the missing checks that prevents the failure.

:issue:`2619`

Fix enforced rotation energy output
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""


Fixes to improve portability
^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Fix nvcc host compiler check triggering
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

:issue:`2583`


Report up to date hwloc version information
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

:issue:`2591`


Disable single compilation unit with CUDA 9.0
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

:issue:`2561`


Miscellaneous
^^^^^^^^^^^^^

Avoid aborting mdrun when GPU sanity check detects errors
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

:issue:`2415`


Improve OpenCL kernel performance on AMD Vega GPUs
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
The OpenCL kernel optimization flags did not explicitly turn off denorm handling
which could lead to performance loss. The optimization is now explicitly turned
on both for consistency with CUDA and performance reasons.
On AMD Vega GPUs (with ROCm) kernel performance improves by up to 30%.


