The ff99SBnmr1 force field was optimized by a conformational reweighting procedure starting from ff99SB using NMR chemical shifts as input. For more information see D.-W. Li and R. Brüschweiler, Angewandte Chemie International Edition (online).
Instruction for Amber 9:
1. Download and move to your Amber "$AMBERHOME/dat/leap/parm" directory.
2. Type command "loadAmberParams frcmod.ff99SBnmr1" in leap terminal before loading of PDB file.
Instruction for Gromacs4.0.7:
1. Download and move to your "gromacs/top/" directory.
2. Increment the number at the top of the "top/FF.dat" file by 1 and add a new line to gromacs/top/FF.dat. like this "ffamber99SBnmr1 NMR optimized protein force field from Amber99SB".
3. Locate the GMXRC in your GROMACS distribution and run `source GMXRC`.
Click here to learn more about Amber port to Gromacs.