in the directory nwchem-6.6/QA/tests/tce_gradients run:
>grep step h2o_ccsd.out
Finite difference step 1.00000D-02
step 1 energy -75.01249910
step -1 energy -75.01184346
step 2 energy -75.01160864
step -2 energy -75.01279302
step 3 energy -75.01082691
step -3 energy -75.01356776
TCE gradient implemented by numerical differentiation.