# GROMACS 2018.5 release notes¶

This version was released on TODO, 2018. These release notes document the changes that have taken place in GROMACS since version 2018.4, to fix known issues. It also incorporates all fixes made in version TODO and earlier, which you can find described in the Release notes.

## Fixes where mdrun could behave incorrectly¶

### Fixed numerical derivative for normal-mode analysis with shell code¶

Due to higher precision needs when using polarizable shell particles the normal mode code did not work reproducibly with shells. In order to fix this the step-size used for numerically computing the Hessian was reduced to near machine precision. The change does not affect the results for non-polarizable systems, such as proteins or small molecules.

## Miscellaneous¶

### Warn for problematic coupling times with Nose-Hoover and Parrinello-Rahman¶

When combining the Nose-Hoover and Parrinello-Rahman coupling algorithms, resonances in the kinetic energy and pressure/volume can appear when the two coupling times involved are similar. Now grompp warns when tau-p is less than two times tau-t.

 issue: 2749

### Fixed efficiency issue with shell code minimization¶

Code cleanup touching unnecessarily complex code created an efficiency issue. Both the issue and some of the complexity are now fixed.

 issue: 2705