AMBER Force Fields Parameters for E64
[1] AMBER force fields parameters for a stand-alone E64 that is NOT covalently bonded to another molecule
[2] AMBER force fields parameters for E64 covalently bonded to 'S' atom of CYS

Use Case
The needed force fields parameters can be loaded to tLeap (that comes with AmberTools) using either of the following two commands.

[A] loadamberparams force_fields_parameters_for_stand_alone_e64.frcmod
[B] loadamberparams force_fields_parameters_for_e64_bonded_to_s_of_cys.frcmod