I would like to perform a geometry optimization for a weakly bound methane dimer structure with Gaussian 16. During this process, the Newton-Raphson step size should be controlled such that its length should not exceed 0.01 bohr. For this purpose, I created the following input (strictly for testing purposes):

%nprocs=120

%chk=test

%mem=100GB

#hf/sto-3g opt=(trustupdate,nrscale,maxstep=1,maxcycles=100,tight)

test

0 1

C 0.000000000 0.000000000 -1.821797542

H 0.000000000 0.000000000 -2.931818538

H -0.906328348 0.523268916 -1.451790544

H 0.906328348 0.523268916 -1.451790544

H 0.000000000 -1.046537831 -1.451790544

C 0.000000000 0.000000000 1.821797542

H 0.000000000 0.000000000 2.931818538

H -0.906328348 -0.523268916 1.451790544

H 0.906328348 -0.523268916 1.451790544

H 0.000000000 1.046537831 1.451790544

Here `maxstep=1` should restrict the NR step below 0.01 bohr. Nevertheless, in the 9th step, I received the following report on convergence:

Item Value Threshold Converged?

Maximum Force 0.001795 0.000015 NO

RMS Force 0.000287 0.000010 NO

Maximum Displacement 0.079485 0.000060 NO

RMS Displacement 0.024807 0.000040 NO

It seems to me that the 0.01 bohr criterion is not fulfilled for the optimization displacement. Is there any way to really constrain the step length during optimization?

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