New and improved features¶
Collective variables module (Colvars) update¶
The (Colvars) library for enhanced sampling simulations included in GROMACS has been updated to version 2025-10-13.
This update brings many improvements, including: - performance improvements for moving frame of reference calculations - improved OPES implementation - improved moving restraint logic, allowing for moving harmonic walls - more flexible definitions of grids on CVs A complete list of changes can be found here.
For documentation see this section of the GROMACS doc along with the Colvars documentation page dedicated to GROMACS 2026. Messages about Colvars in the GROMACS discussion forum should be tagged with the colvars keyword for easier consultation.
Added LEaP-compatible dihedral reordering¶
AMBER LEaP reorders (improper) dihedrals when processing the topology, alphabetically
by atom type. In order for GROMACS to be able to match the topology produced by LEaP,
gmx grompp was extended LEaP-compatible dihedrals reordering. This functionality
is intended for usage with the ports of recent AMBER force fields (e.g. ff14SB and
ff19SB), but it is enabled on any force field that defines the
_FF_AMBER_LEAP_ATOM_REORDERING macro.
This feature has been validated on all supported dipeptides and tripeptides as well as select tetrapeptides and pentapeptides. Systematic validation on a broader set of scientifically relevant biomolecules is still pending.
Added the port of AMBER’s ff14SB and ff19SB protein force fields¶
The latest AMBER force field for proteins, ff19SB, has been ported to GROMACS. The port encompasses all functional forms, including per-amino-acid CMAPs, which are a new feature of ff19SB. Furthermore, the port also includes the recommended optimal 4-point and 3-point charge water models, better known as OPC and OPC3, and matching ions.
Older AMBER force field, ff14SB, has also been ported. For it, the TIP3P and TIP4PEW are considered to be the recommended water models.
Due to the limited usage for production simulations thus far and possible bugs in GROMACS features that these force fields use, these ports are considered validation pending.
Changed the behaviour of pdb2gmx -rtpres¶
In order to support force fields like AMBER19SB, pdb2gmx can now
automatically rename residues to have the name of the chosen residue type, so that
grompp can assign the CMAP terms correctly. This is handled by
a new field in the [ bondedtypes ] description in the residue types database
that specifies that such force fields must rename the residues accordingly.
gmx pdb2gmx -rtpres now defaults to auto, which means to preserve the residue name
unless that residue-type-database setting requires renaming to match the residue type.
It may also be set manually to no or yes.
Improved implementation of the neural network potential interface¶
The neural network potential (NNP) interface has been extended to support new model inputs. Firstly, it is now possible to use a list of atom pairs within the NNP region filtered by a user-specified cutoff, as well as corresponding periodic shift vectors, as an input to the NNP. This enables the use of model architectures such as SchNet or MACE and re-uses the pair-list generated by GROMACS. Secondly, we also add support to pass positions and charges of the MM region around the NNP region to the model, enabling the use of electrostatic embedding schemes such as implemented in EMLE. Furthermore, a link atom scheme is now employed to treat covalent bonds between the NNP and MM regions. In addition, there have been minor performance improvements, and the interface now supports both CUDA and ROCm/HIP-builds of LibTorch. For more details on the supported features and usage, please see the NNPot section in the reference manual.
Added support for H5MD trajectory file format¶
Trajectory data can now be written to the H5MD file format by gmx mdrun. Data written to this file format includes positions, velocities, forces, and the simulation box. Chemical bonds are also written to the connectivity group. For this release, only lossless output is supported.
Note that support for this file format in GROMACS tools is experimental. Analysis tools are able to read all files but bugs should be expected. H5MD output from gmx trjconv and gmx trjcat is not implemented.
Fast Multipole Method (FMM) interface support¶
Support for simulations with external FMM libraries has been added. Short-range electrostatics can be computed by either GROMACS or the FMM library, while long-range electrostatics are handled by the FMM library when an FMM backend is selected. Although the FMM interface allows short-range electrostatics to be configured for either GROMACS or the FMM backend, short-range FMM interactions support in GROMACS is planned but not part of this release. MDP options are available for the well-known FMM libraries i.e., ExaFMM and FMSolvr, and these options are validated internally by the interface.
For more details, please see the FMM section in the reference manual. Add two new performance metrics “””””””””””””””””””””””””””””””
gmx mdrun reports two additional time step-independent metrics to measure the performance of a simulation on specific hardware. The ms/step is the average wall-clock time (in milliseconds) required to compute a single timestep. As a direct measure of computational cost per timestep, it is useful for profiling code or hardware performance for a specific system. Matom*steps/s considers the number of atoms and measures the throughput of actions (number of steps * number of atoms) per second. This metric is suitable when comparing performance across systems and hardware. A similar metric can also be found from PLUMED.