Hi. I am new to DFT and using ORCA to run calculations of IR and NMR spectra for small (around 30 atoms) organic molecules. I am using and input like:

! M062X TZVP def2/J def2/JK RIJCOSX GridX4 Grid5 FinalGrid6 D3zero TightOpt TightSCF NMR NumFreq

%FREQ SCALFREQ 0.9462 END

%geom

Calc_Hess true NumHess true

MaxIter 500

end

I´ve noticed that this keyword Calc_Hess true forces to run a first Hessian calc and the vibrational freqs at the beginning, before the geometry optmization, and this is a quite time consuming step, and then again at the end after the optimum geom is found.

I am not interested in transition states, so I wonder if:

can remove this CALC_HESS keyword without losing quality to my IR and NMR results?