I used ORCA and now, I change into Gaussian 09 because my professor (and other researchers) like it. However, I find that the tutorial of this software is not good, even though I try to find it a lot.

I have read the support in the main website, but they only describe the content of each keyword. They don't have any good example, that is my problem.

For example, with my model (N-heterocyclic carbene + graphene), they consist about ~ 150 atoms and I try first with B3LYP, fail. I continue with PB86, it still fail (convergence failure). Then, I decide to use low method, namely PBE but I don't know how to code it, no basis set can do that.

# opt PBE/STO

# opt PBE/STO-3G

# opt PBE/STO-TZ2P

I try all of them, fail. What should I do? And, in the future, when I have problem with keyword, how can I find the solution?

'...We employed the triple-ζ

Slater basis set, plus two polarization functions (STO-TZ2P)

for valence electrons, within the generalized gradient

approximation (GGA) according to the Perdew−Burke−

Ernzerhof (PBE) nonlocal exchange-correlation functional..." (here is the method I want to follow, but I don't now how to use it)

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