# GROMACS 2016.1 Release Notes¶

This version was released on October 28, 2016. These release notes document the changes that have taken place in GROMACS since the initial version 2016 to fix known issues. It also incorporates all fixes made in version 5.1.4.

## Made distance restraints work with threads and DD¶

The NMR distance restraints use several buffers for summing distances that were indexed based on the index of the thread+domain local ilist force atoms. This gives incorrect results with OpenMP and/or domain decomposition. Using the type index for the restraint and a domain- local, but not thread-local index for the pair resolves these issues. The are now only two limitations left:

• Time-averaged restraint don’t work with DD.
• Multiple copies of molecules in the same system without ensemble averaging does not work with DD.

Note that these fixes have not been made in any 5.1.x release.

## Fixed Ewald surface+3DC corrections¶

Ewald surface and 3DC correction forces were only applied up to, but not including, the last atom with exclusions. With water at the end of the system only the last H would not be corrected. With ions at the end all ions would be missing. In addition, with the Verlet scheme and domain decomposition no force correction was applied at all.

Issue 2040

Issue 2033

## Fixed bug in gmx insert-molecules.¶

With option -ip, and if all trials were unsuccessful, a molecule was eventually incorrectly placed at 0/0/0 due to a memory error when referencing to rpos[XX][mol].

## Made virial reproducible¶

OpenMP reduction was used to reduce virial contributions over threads, which does not have a defined order. This leads to different rounding, which makes runs non-reproducible (but still fully correct). Now thread local buffers are used. Also removed OpenMP parallezation for small count (e.g. shift forces).

## Updated to support FFTW 3.3.5¶

The auto-download of FFTW now gets FFTW 3.3.5 and builds it properly, including with --enable-vsx when GMX_SIMD is set to VSX, i.e. for Power8, and --enable-avx512 when GMX_SIMD is any of the AVX flavours (which is safe on non-512 now, works on KNL, and is presumed useful for future AVX512 architectures).

## Permitted automatic load balancing to disable itself when it makes the run slower¶

Under certain conditions, especially with (shared) GPUs, DLB can decrease the performance. We now measure the cycles per step before turning on DLB. When the running average of cycles per step with DLB gets above the average without DLB, we turn off DLB. We then measure again without DLB. If without DLB the cycle count is still lower, we keep DLB off for the remainder of the run. Otherwise is can turn on again as before. This procedure ensures that the performance will never deteriorate due to DLB.

## Improved the accuracy of timing for dynamic load balancing with GPUs¶

With OpenCL, the time for the local non-bonded to finish on the GPU was ignored in the dynamic load balancing. This change lets OpenCL take the same code path as CUDA.

One internal heuristic parameter was far too small for both CUDA and OpenCL, which is now fixed.

## Corrected kernel launch bounds for Tesla P100 GPUs¶

This corrects our initial guess of kernel tuning parameters that resulted in reduced occupancy on sm_60 GPU, and thus improves performance.

## Improved logic handling if/when the run is terminated for SETTLE warnings¶

The code now honours that when the environment variable GMX_MAXCONSTRWARN is set to -1, there is no maximum number of warnings.

Issue 2058

## Fixed bug in gmx wham for reading pullx files.¶

Because the order of columns in the pullx files has changed recently, gmx wham did not pick the reaction coordinate from pullx.xvg if the COM of the pull groups were written. gmx wham was tested with various pull options and geometries.

## Fixed deadlock with thread-MPI¶

With thread-MPI mdrun could deadlock while pinning threads.

Issue 2025

## Made error reporting in grompp more user friendly¶

This tool now always reports the file and line in user input files that lead to a condition such that subsequent parsing cannot continue.

## Fixed default nice level in mdrun-only build¶

Now an mdrun-only build should default to zero nice level, the same as gmx mdrun in a normal build.

## Fixed math-test false positive¶

Depending on the accuracy of the floating point division, the input of the test function could be 1ulp too large or too small. If it was too large the result of the test function wasn’t within 4ulp and the test failed.

## Improved documentation¶

Approaches for reducing overhead for GPU runs are now documented.

The available wallcycle counters and subcounters reported in the md.log files are now listed and and explained in the user guide, along with how to enable reporting of the subcounters.

Several install-guide sections have been improved, including those for OpenCL, mdrun-only, and “make check”. A “quick and dirty” cluster installation section was added.

## Removed variable-precision .gro writing¶

The precision used when writing .gro files is now fixed to 3, 4 and 5 decimal places for x, v and box respectively to ensure compatibility with other software. Variable-precision reading is still supported.

Issue 2037

## Fixed BG/Q platform files and install guide¶

Renamed the platform file to reflect normal practice and the install guide.

## Reduced the memory required for free-energy simulations¶

Pair lists with atoms whose short-ranged parameters are perturbed now use less memory.

Issue 2014