Hi,

I'm just learning to use QuantumATK for my thesis work. I need to simulate organic molecules which contain 5500-15.000 atoms. Therefore DFT does not seem to be feasible due to the large number of atoms. I turned to Semi-Empirical method and it also does not seem to be capable of converging with such number of atoms. Today I was reading the QuantumATK manual pages and came across the following paragraph:

"Note

**The HÃ¼ckel parameters have been fitted for non-self-consistent calculations.** To use the parameters in self-consistent calculations, the self-consistent onsite shifts must be compensated by a reverse shift of the vacuum_levels."

on page:

https://docs.quantumatk.com/manual/SE.html.

Combining this expression with the fact that the no SCF checkbox is checked by default in Semi-Empirical Calculator, can we say that the results of

**non-self-consistent calculations** with Semi Empirical Calculator in QuantumATK are valid and accurate? In other words, are the results of no SCF Semi-Empirical calculations valid? I understand that self-consistent field is no doubt more accurate but given the very large number of atoms, can the results of non-self-consistent Semi Empirical package be considered valid for a thesis or publication work?

Thanks,

K. Cerda