Using Custom Force Field Parameters in FEP+

Custom force field parameters generated by the Force Field Builder - OPLS4/OPLS5 Panel can be used in FEP+ calculations to improve the accuracy of torsion potentials for your ligands.

Locating custom parameters

Custom parameters are stored in a file with a name of the form custom_release.opls. By default, this file is saved in the opls_dir folder in your User resources directory ($HOME/.schrodinger/opls_dir/ on Linux and Mac). You can change the default location in the Force Field settings section of the Preferences Panel, or set a project-specific location in the Set Custom Parameters Location Dialog Box.

Using custom parameters in Maestro

To use custom force field parameters when running an FEP+ job from the FEP+ Panel:

  1. Click the Settings button to open the FEP+ Settings Dialog Box.
  2. In the Force Field section, select Use customized version.
  3. Click the parameter set button to open the Set Custom Parameters Location Dialog Box, where you can browse to the directory containing your custom .opls file.

If you want custom parameters to be selected by default in all panels, select Use custom parameters by default in the Force Field settings section of the Preferences Panel.

Using custom parameters from the command line

To use custom force field parameters when running fep_plus from the command line, use the -OPLSDIR flag to specify the directory containing your custom .opls file:

$SCHRODINGER/fep_plus other-options -OPLSDIR /path/to/opls_dir

The -OPLSDIR flag should also be included when restarting FEP+ jobs. See Troubleshooting Common Issues for an example of a restart command.

For a full list of fep_plus command-line options, see fep_plus Command Help.

Merging custom parameters

If you have run the Force Field Builder multiple times and have parameters saved in different locations, you can merge them into a single custom force field using the custom_params Command Help utility.

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