Using DC vs HF-DFT

Questions
#1

Hi all,

I am interested in using DC_DFT and just wanted to understand this better. Am I expected to get the same result using the DC_DFT keyword vs doing a two-step job converging with HF first and then using SCF_GUESS READ to do the one iteration with DFT?

Thank you!

#2

Not necessarily. In the latter calculation, you need to be careful because Q-Chem will try to do two SCF cycles, which is the minimum number to make sure F and P are consistent. And depending on the options, sometimes your guess orbitals get processed (e.g., with purification or a Roothaan step).

#3

Thanks for your quick response!