# Bugs fixed¶

## Fixed multiple time stepping with Parrinello-Rahman and Nose-Hoover.¶

These now work in correct Trotter style, applied once and scaled by the correct number of steps.

Fixes Issue 2031 Fixes Issue 2032

## Applied Berendsen pressure coupling only at nstpcouple steps¶

Berendsen pressure coupling was mistakenly applied on successive steps. Since there is no need for this, this is changed to act only on nstpcouple steps. Note that this change prevents continuation from old checkpoint files for Berendsen pressuring-coupling runs, since the previous-step pressure is no longer stored.

## Added missing Ewald correction for PME-User¶

With coulombtype=PME-User, the Ewald mesh energy was not subtracted leading to (very) incorrect Coulomb energies and forces.

Fixes Issue 2286

## Fixed incorrect dV/dlambda for walls¶

The free-energy derivative dV/dlambda for walls, which can be perturbed by changing atom types of non-wall atoms, only contained the B-state contribution.

Fixes Issue 2267

## Supported OpenMP for orientation restraints¶

Previously this was broken, but has been fixed and is now tested and supported.

## Fixed orientation restraint reference¶

The resetting of the COM of the molecule with orientation restraints for fitting to the reference structure was done with the COM of the reference structure instead of the instantaneous structure. This does not affect the restraining (unless ensemble averaging is used), only the printed orientation tensor.

Fixes Issue 2219

## Used graph with orientation restraints¶

With the Verlet cut-off scheme by default molecules are not made whole. Now they are made whole when orientation restraints are used. Added checks and assertions for correct PBC treatment with orientation restraints.

Fixes Issue 2228

## Fixed Ekin at step 0 with COM removal¶

The kinetic energy at step 0 was computed from the velocities without the center of mass velocity removed. This could cause a relatively large jump in kinetic energy, especially for small systems. Now compute_globals is called twice with COM removal so we get the correct kinetic energy.

## Fixed gmx grompp with Andersen massive and no COM removal¶

Fixed a floating point exception leading to a segv. Also fixed possible different rounding for the interval for Andersen massive in gmx grompp in mdrun for the common case where tau-t is a multiple of delta-t.

Fixes Issue 2256

## Improved Verlet buffer constraint estimate¶

The displacement estimate for a constrained atom (typically H) rotating around the COM with a partner atom is now derived and documented correctly. Note that we (still) use a Gaussian with matched variance, which results in a much larger buffer than necessary, since the tail of the displacement distribution sets the buffer size and the Gaussian has a long tail whereas the actual distribution has no tail.

## Fixed virtual site generation for water oxygens not named OW¶

gmx pdb2gmx would break when generating virtual sites if water oxygens were not named OW. Now checking for the atomnumber instead.

Fixes Issue 2268

## Fixed thread-MPI rank choice for orientation restraints¶

Only a single rank is supported, so that must be what the thread-MPI code will choose. There’s another check later on that catches the multi-rank MPI case.

## Fixed some incorrect behavior with gmx solvate¶

gmx solvate cannot replicate non-rectangular solvent boxes correctly (there are several different places that assume a diagonal box matrix), so give a fatal error if that is attempted. To support some uses with triclinic boxes, skip the replication step if the solvent and target box sizes are already equal.

Support for general triclinic boxes can be added separately, and the check introduced here can be valuable even in that case: it keeps a pre-equilibrated solvent box intact if the target box size is the same.

Related to fix of Issue 2148

## Fixed DD exact continuation in reproducible node¶

With domain decomposition, the local atom density, used for setting the search grid for sorting particles, was based on the local atom count including atoms/charge groups that would be moved to neighboring cells. This lead to a different density value, which in turn could result in a different number of search grid cells and thus a different summation order during a run compared with continuing that run from a checkpoint, when no atoms would be moved. That difference violated the intention of mdrun -reprod, and is now fixed.

Refs Fixes Issue 2318

## Made mdrun only stop at nstlist steps with mdrun -reprod¶

Stopping mdrun with two INT or TERM signals (e.g. from Ctrl-C from the terminal shell) would always happen right after the first global communication step. But this breaks exact continuation. Now with mdrun -reprod a second signal will still stop at a pair-list generation step, like with the first signal, so we can still have exact continuation.

Fixes Issue 2318

## Added check for GPU detection support before detecting GPU devices¶

When a CUDA-enabled binary was run on a node with no CUDA driver available, a note was issued that the version of the CUDA driver is insufficient, which was wrong and now fixed.

Fixes Issue 2322

## Removed duplicated lines from OPLS ffbonded.itp¶

Identical lines have been removed, as identified with uniq.

Fixes Issue 1678.

## mdrun no longer warns about NVML clocks that are at max¶

If the clocks are already maxed out there is no point in echoing warnings about not being able to set them.

Fixes Issue 2313.

## Used reduced default tolerances for tpx comparison¶

The tolerances for gmx check are mainly intended for handling slight statistical deviations, but they can hide differences between tpr files, when the user likely wants exact checks on small quantities like Lennard-Jones parameters. This changes changes the default relative tolerance to 0.000001 and the absolute tolerance to zero, so that we only allow for any minor differences due to compiler optimization.

Fixes Issue 2024.

## Fixed return values of frame-reading functions¶

This function was based on read_first_x that returned the number of atoms, and was documented to do the same, but has always returned a logical boolean about whether a frame has been read. This led to aspects of gmx spatial and gmx trjcat -demux being broken.

Fixed by returning a proper bool, and fixing the remaining logic that used the return value in a non-boolean sense.

Refs Issue 2157

## Removed PBC before generating TPR with group scheme¶

Ensure that all molecules have been made whole before generating the run input file when using the group scheme, to avoid error messages for large charge groups when molecules are broken over PBC boundaries.

Fixes Issue 2339

## Fixed PBC error in gmx_spatial¶

Fixes Issue 2157.

## Documented power spectrum options of gmx velacc¶

Fixes Issue 2019.

## Changed to require .tpr file for gmx cluster¶

The program could crash without it, so it wasn’t optional.

Fixes Issue 2170.

## Disallowed ascii formats for gmx trjcat¶

Since gmx trjcat (deliberately) does not use any .tpr file, the tool can’t handle trajectory formats such as .gro or .pdb where atom/residue names are needed.

Fixes Issue 2225.

## Improved grompp missing-parameters error message¶

If an interaction entry had parameters but not the function type, then the error message has been confusing. Note that even when only one function type is implemented, the field is still required, which makes for ready extensibility.

Refs Issue 2144

## Checked for large energy at first step¶

Also added step number to fatal error message.

Fixes Issue 2333

Fixes Issue 2332

## Avoided confusing message at end of non-dynamical runs¶

Energy minimization, test-particle insertion, normal-mode analysis, etc. are not targets for performance optimization so we will not write performance reports. This commit fixes an oversight whereby we would warn a user when the lack of performance report is normal and expected.

Fixes Issue 2172

## Changed to require -ntmpi when setting -ntomp and using GPUs¶

With GPUs and thread-MPI, setting only gmx mdrun -ntomp could lead to oversubscription of the hardware threads. Now, with GPUs and thread-MPI the user is required to set -ntmpi when using -ntomp. Here we chose that to also require -ntmpi when the user specified both -nt and -ntomp; here we could infer the number of ranks, but it’s safer to ask the user to explicity set -ntmpi. Note that specifying both -ntmpi and -nt has always worked correctly.

Fixes Issue 2348