The simulation runs—but is it using the GROMACS you intended?

A molecular dynamics workflow can depend on more than the structure and simulation parameters. The GROMACS executable and force-field files selected for a local run matter too. This becomes especially important when you need a particular GROMACS version for reproducibility, or when your machine already has a GROMACS installation that you want to use.

GROMACS Wizard includes a packaged GROMACS version, but it also lets you configure a locally installed version for local computations. Here is a practical way to check that setup—and to understand which performance settings affect your run.

Choose the executable and force-field directory together

In GROMACS Wizard, open Settings and select Use a different GROMACS version. You will need to provide two paths:

• The GROMACS executable: gmx.exe on Windows, or gmx on Linux and macOS.
• The force-fields folder: the directory containing the forcefield.ff folders. For example, the documentation gives $HOME/gromacs/share/top/ as a Linux or macOS example.

These are separate choices: pointing to the executable alone is not the complete configuration. Check that the selected force-fields directory is the one you intend to use as well. GROMACS Wizard displays the detected version when it recognizes the executable; if it cannot recognize it, the version is shown as invalid. Treat that display as a useful configuration check before launching a calculation.

Once you have selected the paths, take a moment to record the GROMACS version and force-field location alongside your project notes if reproducibility matters. That simple habit can make it easier to understand later which local setup was used.

Performance settings: local means local

GROMACS has built-in mechanisms for making use of hardware, and its automatic choices may be sufficient for many workloads. GROMACS Wizard also allows additional local performance parameters, including options such as ntmpi, ntomp, pme, and maxh. These can help you configure parallelization and other aspects of mdrun, but changing them is not automatically an improvement. If a run is working well, there may be no need to override the defaults.

By default, the Wizard sets the number of threads for local jobs below the absolute maximum so your machine can remain responsive while a job runs. A thread count of 0 lets GROMACS choose automatically. If you specify a non-zero value below the number of logical cores, GROMACS Wizard also uses -pin on to improve thread placement.

Important distinction: these performance parameters apply only to local jobs; they are not sent with Cloud jobs. If your goal is to tune a cloud calculation, changing the local performance settings will not do that.

Use -maxwarn with care

The -maxwarn option can let gmx grompp continue despite warnings that would otherwise stop execution. A warning is not necessarily harmless: the documentation advises interpreting the messages carefully, since bypassing them may produce an unstable system. One example described there is a GROMOS force-field warning that can be bypassed by setting -maxwarn to 1. This option applies to both local and Cloud jobs, unlike the local performance parameters.

A sensible order of operations is: verify the executable and force-field directory, read any preprocessing warnings, and only then decide whether an override is appropriate. Use performance overrides when you have a specific reason to change local behavior, rather than as a first response to an unexpected run.

For the complete instructions and related settings, see the GROMACS Wizard settings documentation.

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