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?
Dear Roland
It is neccesary to revise the IOP reference list to find the required keyword that you need. Additional control of gaussian algorithms is only requested by ioPs in the keyword line according to the overlay that you need to modify.
https://gaussian.com/iops/
Regards
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