<div dir="ltr">Dear all, following my previous post (huge number of imaginary frequencies...) on this issue, I have in the meantime tried to break down to problem into a smaller one.Basically, instead of using the full bulk system, I have tried a simple optimization and frequency calculation on one of the cationic portions (organometallic complex) of the system. I have used a cubic cell with a = 20 Ang. I have made sure that the structure for the subsequent vibrational analysis job does indeed correspond to the final structure of the optimization run (I have included ATOMIC_COORDINATES ON to print out the geometry in the output). Again, in the first attempt (using DX 0.001) I end up with a huge number (~50) of imaginary frequencies, including some very large ones. VIB| NORMAL MODES - CARTESIAN DISPLACEMENTS VIB| VIB| 1 2 3 VIB|Frequency (cm^-1) -4133.188102 -2206.847291 -2036.718924 VIB|Intensities 0.326216 0.395802 0.125908 VIB|Red.Masses (a.u.) 1.746454 1.699628 1.961778 VIB|Frc consts (a.u.) -1.304878 -0.103208 -0.086426 Now, if I repeat the same calculation with a larger DX of 0.01, I end up with less imaginary modes, but still too many (17) to trust the result. Also, massive change now in the magnitude of the wavenumbers, which drops to -957 cm-1 for imaginary mode nr 1. Think the details here are not so relevant, but I am quite confused. So the problem is not related to the bulk system, but intrinsically related to the vibrational analysis protocol I am following at the moment. Also, as far as the SCF is concerned, I am using inner / outer SCF in combination with DIIS. Apparently the very first SCF never converges after 100 steps, which is when the outer SCF kicks in and from there everything seems to converge smoothly. Maybe my thinking is wrong here? This is what it looks like (in condensed form) from one of the replica outputs: rhdcpenba_mol_vib-r-9.out: *** SCF run NOT converged *** rhdcpenba_mol_vib-r-9.out: *** SCF run converged in 15 steps *** rhdcpenba_mol_vib-r-9.out: *** SCF run converged in 4 steps *** rhdcpenba_mol_vib-r-9.out: *** SCF run converged in 6 steps *** rhdcpenba_mol_vib-r-9.out: *** SCF run converged in 6 steps *** rhdcpenba_mol_vib-r-9.out: *** SCF run converged in 8 steps *** rhdcpenba_mol_vib-r-9.out: *** SCF run converged in 9 steps *** rhdcpenba_mol_vib-r-9.out: *** SCF run converged in 8 steps *** rhdcpenba_mol_vib-r-9.out: *** SCF run converged in 9 steps *** rhdcpenba_mol_vib-r-9.out: *** SCF run converged in 9 steps *** rhdcpenba_mol_vib-r-9.out: *** SCF run converged in 10 steps *** rhdcpenba_mol_vib-r-9.out: *** SCF run converged in 10 steps *** rhdcpenba_mol_vib-r-9.out: *** SCF run converged in 13 steps *** rhdcpenba_mol_vib-r-9.out: *** SCF run converged in 13 steps *** rhdcpenba_mol_vib-r-9.out: *** SCF run converged in 14 steps *** rhdcpenba_mol_vib-r-9.out: *** SCF run converged in 15 steps *** rhdcpenba_mol_vib-r-9.out: *** SCF run converged in 16 steps *** rhdcpenba_mol_vib-r-9.out: *** SCF run converged in 15 steps *** rhdcpenba_mol_vib-r-9.out: *** SCF run converged in 15 steps *** rhdcpenba_mol_vib-r-9.out: *** SCF run converged in 15 steps *** rhdcpenba_mol_vib-r-9.out: *** SCF run converged in 15 steps *** rhdcpenba_mol_vib-r-9.out: *** SCF run converged in 15 steps *** rhdcpenba_mol_vib-r-9.out: *** SCF run converged in 14 steps *** rhdcpenba_mol_vib-r-9.out: *** SCF run converged in 14 steps *** rhdcpenba_mol_vib-r-9.out: *** SCF run converged in 15 steps *** So my question really is, how do I choose an appropiate value for DX (and other parameters), and what is potentially going wrong here. I am absolutely clueless I must say, since I considered this as an 'easy' task. I feel that I am just simply doing something wrong, although I thought I was following standard procedure. I am keeping all other values such as SCF convergence and so on untouched, in order to not introduce any inconsistencies here. Would a more rigorous optimisation perhaps be helpful? Thanks for your help, much appreciated. Files attached. Best Tobi </div>