# Improvements to GROMACS tools¶

For now, this tool only plots coordinates, velocities, and forces for selections, so it should provide a full replacement for -ox, -ov, -of, -com, and -mol from gmx traj.

## Made TNG writing work with multiple identical steps¶

Introduce a wrapper structure around TNG so we detect and correct for cases when writing multiple frames with the same step, or non-zero initial steps to TNG files. This will avoid frames overwriting each other, and make sure the time per frame is correct.

Issue 2189

## Improved frame time/step handling in gmx trjconv¶

Store the exact step in PDB/GRO file headers, and be more careful about not claiming to have time or step information when it was not available. This change will avoid some of the problems described in Issue 2189, but it does not yet properly fix the issue in the TNG library.

Issue 2189

## Fixed gmx trjconv to always dump at correct time¶

Set frame timestep before starting the loop by reading first two frames and rewinding, and make sure we always write something to the dump output based on best-guess (if there is at least one input frame present).

Issue 1832

## Clarified gmx editconf help text¶

It is possible that users can confuse -c with -center so this patch makes it clear that -center doesn’t do anything unless the user really wants to shift the center of the system away from the middle of the box.

Fixes Issue 2171

Fixes Issue 2272

## Removed incorrect comment for CHARMM tips3p¶

Removed CHARMM tips3p performance warning in gmx pdb2gmx input file, since the performance loss is negligible with the cutoff-scheme=Verlet.

## Avoided gmx grompp charge warning from merely rounding error¶

Even though the gmx grompp total charge check uses double for summation, there are rounding errors for each charge when charges are stored in single precision. Now the charge check rounds the net charge of molecules to integer when the difference is less than the maximum possible sum of charge rounding errors.

Fixes Issue 2192

## Improved pdb2gmx for nonstandard residue types¶

If explicit non-blank chain identifiers are set, it will now be a hard error if the residue types in each chain do not match. For blank chain ID we still need to allow detection of non-chain parts, but this case too now provides more explicit output information.

Issue 2370

## Allowed empty lines in hdb files¶

Skip lines that consist only of whitespace. Not a universal solution for fixing hdb files, but better than the user getting very strange error messages that don’t say anything about whitespace.

Issue 2028

## Changed to no longer require matching names between rtp and tdb files¶

This was only documented in the source. It’s a remnant from the days when all force fields were in the same directory, and no longer necessary. With this change we will properly match all termini to all amino acids.

## Made duplicate atoms in bondeds an error in gmx grompp¶

Having duplicate atom indices in bonded interactions used to be only a warning. But since in nearly all cases this will lead to issues, this is now a error, except for angle restraints where it can be useful so there it is now a note.

Issue 2141

## Made gmx grompp -r obligatory with position restraints¶

With position restraints it would often occur that users accidentally used equilibrated coordinates instead of the original coordinates for position restraint coordinates due to -r defaulting to -c. Now -r always need to be supplied with position restraints, but using the same file name as with -c will reproduce the old behavior.

## Fixed gmx msd when using COM removal and molecules¶

Changed order of code to actually assign correct coordinates before copying the data, and modified data structure size when using COM removal and individual molecules.

Issue 2043

## Fixed index error in gmx chi¶

An error in the index construction could lead to segfaults. However, the actual indices were correct, so it should not have produced any incorrect results.

Issue 1814

## Fixed gmx grompp complexity for large exclusion orders¶

To avoid exploding computational complexity for highly connected molecules with large values for excluded neighbors, avoid adding a neighbor to the temporary nnb structure if it is already present as a lower-order neighbor.

Issue 2260

## Fixed gmx density for non-mass calculations¶

We now always use mass and never charge/electron density to center systems.

Issue 2230

Fixes Issue 2279