GROMACS 2026.1 release notes
----------------------------

This version was released on March 6th, 2026. These release notes
document the changes that have taken place in |Gromacs| since the
previous 2026.0 version, to fix known issues. It also incorporates all
fixes made in version 2025.4 and earlier, which you can find described
in the :ref:`release-notes`.

.. Note to developers!
   Please use """"""" to underline the individual entries for fixed issues in the subfolders,
   otherwise the formatting on the webpage is messed up.
   Also, please use the syntax :issue:`number` to reference issues on GitLab, without
   a space between the colon and number!

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

Fixed a performance issue with thread-MPI
"""""""""""""""""""""""""""""""""""""""""

Way too many OpenMP threads (up to approximately (number_of_cpu_cores)^2) could be created,
severely impacting performance.

:issue:`5564`

Fix segfault on exit when running NNP inference with CUDA
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

When running a simulation with the NNPot interface and performing inference on a CUDA device,
a segfault would occur on program exit. This did not affect results, but should not happen.

:issue:`5568`

Running perturbed non-bonded interactions on a GPU could cause crashes
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

With atoms with small Lennard-Jones sigma parameter or no Lennard-Jones
interactions, running perturbed non-bonded interactions on the GPU with
soft-core would lead to extremely large forces. This would make simulations
crash within a few steps.

:issue:`5548`

Incorrect results with perturbed non-bonded interactions on a GPU and many lambda states
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

When running perturbed non-bonded interactions on the GPU, the delta-H values,
and thus free-energy differences, would be incorrect when more than 64 lambda
states were used.

:issue:`5551`

The new AWH histogram tolerance parameter was not printed to the log file
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

Also added it to ``gmx dump``.

:issue:`5574`

Ensemble averaging of orientation restraints gave a fatal error
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

:issue:`5552`

PME tuning never activated with a GPU and a single MPI rank
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

:issue:`5578`
       
Fixes for ``gmx`` tools
^^^^^^^^^^^^^^^^^^^^^^^

``pdb2gmx`` can now prints 7 decimals for charges and masses
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

``pdb2gmx`` would print charges and masses with a maximum of 6 total
decimals. Now this is 7, which matches the floating point precision
for charges and masses.

:issue:`5543`

Fixed ``gmx wham -ac`` autocorrelation time calculation
""""""""""""""""""""""""""""""""""""""""""""""""""""""""

Fixed ``gmx wham -ac`` incorrectly reporting very large integrated autocorrelation times (IACT)
for long umbrella sampling trajectories when the pull coordinate was far from zero,
due to precision loss in the calculation.

:issue:`5547`

Fixes that affect portability
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Fix device arch setup with newer version of amdclang
""""""""""""""""""""""""""""""""""""""""""""""""""""
Newer versions of the compiler would fail to correctly configure the project due
to not treating the test file as HIP input.

:issue:`5558`


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

Do not write user names to H5MD files
"""""""""""""""""""""""""""""""""""""
``mdrun`` now always writes the string "N/A" instead of the user name to
the /h5md/author/name metadata field in H5MD files. 

:issue:`5557`

Correctly detect warp uniform variable in CUDA kernel
"""""""""""""""""""""""""""""""""""""""""""""""""""""
NVCC was failing to detect warp uniform variables leading to performance 
degradation in the non-bonded force kernel. A workaround was implemented. 

:issue:`5546`

QM/MM CP2K MDModule will check orthogonality of the cell
""""""""""""""""""""""""""""""""""""""""""""""""""""""""
QM/MM simulations in CP2K require orthogonal periodic cells. The MDModule 
will now check for orthogonality of the cell and abort if the cell is 
non-orthogonal. In case of user-provided CP2K input files, a warning 
will be issued.

:issue:`5529`

New DFT functionals and D3 dispersion corrections for QM/MM with CP2K
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
QM/MM simulations with CP2K could now use hybrid DFT functionals B3LYP, PBE0 and
range-separated hybrid functionals CAM-B3LYP, wB97X, wB97X-D3 in combination with
all-electrons 6-31G* basis set. In addition, the option of using D3 dispersion 
corrections has been added to all functionals.

:issue:`5529`

Use correct stream priorities with AdaptiveCpp
""""""""""""""""""""""""""""""""""""""""""""""

In |Gromacs| 2026.0 built with AdaptiveCpp 25.02 or earlier, the GPU stream
priorities were inverted. This could have led to decreased performance.

:issue:`5575`

