This question refers to the leaprc files stored in $AMBERHOME/dat/leap/cmd/oldff in distributions of AmberTools.
Before answering the question, it is important to know that files in the oldff directory have been placed there because they are no longer recommended. It isn’t necessarily that those old force fields are terrible; it’s just that the newer ones are significantly better. So, we purposefully make it difficult for novice users to use them. We keep them around primarily for historical purposes.
That said, it is possible to use them. But, you might have to work at it. There is no promise that the files referenced in the leaprc will be in the standard AMBERHOME paths. In fact, in some instances, certain files will be moved out of the standard path for the purpose of complicating use of the old force field.
The best way to use the old force fields is this:
- Make your own local directory of parameters.
- Copy all the required force field files there. You can find names of the relevant files in the leaprc file. But, remember, they might not exist in the expected paths.
- Change the leaprc so that it refers to the files in your local directory rather than to the files in AMBERHOME.
- Use leap as usual to generate your input files.
All current and previously published versions of the GLYCAM force fields are available at: