Once the target molecule T has been chosen, the two main molecular descriptors required for a JOYCE-based QMD-FF parameterizations are its optimized geometry and Hessian matrix. Additionally, if T presents flexible torsions around specific bonds, relaxed and/or rigid torsional energy profiles and related geometries should also be included among the reference descriptors. Finally, in specific cases, [21] the energy gradients along the aforementioned scans can be included to complete JOYCE3.0 reference database.
All structures, their energies, gradients and Hessian matrix should be computed at QM level specifically for the traget compound T and with a unique reference method, being it WF or DFT based.
In older JOYCE's releases, all QM data were stored in a formatted
checkpoint file (.fchk), native for the GAUSSIAN16 [20] package.
JOYCE3.0 code now also reads the QM info from the
3 native .fcc format. [19]
All details about the .fcc format, the codes for which it supplies an interface, the tools to use it and their distribution can be found at the JOYCE3.0 website, [13] or the repository of the code[24], which includes specific documentation.