# Optimization problem for an NO moleclue

Sorry for my recent questions as a beginner.

I also did optimization calculation for NO (a structure was downloaded from here Nitric Oxide | NO | CID 145068 - PubChem )

But, I got the following error during the optimization, could you suggest me how I can fix it?

(by the way, if there is a list for these kinds of issues which were solved alredy, please teach me it. Best regards)

``````level = "hf/sto-3g"
energy, wf = psi4.optimize(level, molecule=molecule, return_wfn=True)

mol_input = 0 1
N 0.7119609710519391 0.0 0.0
O -0.7119609710519391 0.0 0.0

c: [0]
fc: [0.0]
m: [1]
fm: [1]

ValidationError: Inconsistent or unspecified chg/mult: sys chg: None, frag chg: [0.0], sys mult: None, frag mult: [1]

``````

β0 1β cannot possibly describe NO.

There are multiple places you could be stuck on here: understanding what 0 1 means, understand what spin multiplicity means, or knowing what the correct spin multiplicity is. Where are you stuck?

Thank you for the comment for my begunner question.

I used spin multiplicity of 2 for NO, However, optimization process does not converge as follows, even with psi4.set_options({βMAXITERβ: 1000}) # Default is 100

SCFConvergenceError: Could not converge SCF iterations in 1000 iterations.

Are there any tips to avoid the error.

I canβt reproduce the error. Please give me the output file.

psi4_NO_doublets.txt (21.1 KB)

this is ipynb for NO moleclues where the error is shown
thanks

STO-3G is a terrible basis set, which is why converging the wave function to the degree wanted by `optimize` is hard. The optimization works fine in a more reasonable basis set.

You can get the calculation to converge in STO-3G as well with

``````molecule {
0 2
N 0. 0. 0.
O 0. 0. 1.15
}
set reference uhf
set soscf true
optimize('hf/sto-3g')
``````
2 Likes

Thanks for the kind comment, which is very helpfull for me. Calculation was converged.

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