# GROMACS 2018.6 release notes¶

This version was released on February 22, 2019. These release notes document the changes that have taken place in GROMACS since version 2018.5, to fix known issues. It also incorporates all fixes made in previous versions, which you can find described in the Release notes.

## Fixes where mdrun could behave incorrectly¶

### Correct free-energy Delta H output with mass lambda’s¶

When separate lambda parameters were used for perturbed mass free-energy contributions, these contributions were double counted in the Delta H output used for BAR calculations. Note that dH/dlambda was always correct

### Fix incorrect LJ repulsion force switching on GPUs¶

When using a CUDA or OpenCL GPU, the coefficient for the second order term for the LJ repulsion in the force switching function, called ‘A’ in the manual, had the wrong sign. This lead to very small errors in the forces and the pressure. Note that the dispersion force switching was correct. The effects of this bug on any physical results seems to be negligible. Note that force switching is usually only used in combination with the CHARMM force field.

Issue 2845

## Fixes to improve portability¶

### Fix compiler flags for Power8¶

A compiler flag for Power8 processors lead to errors in the code and was removed.