Hello everyone,

I have a - rather basic - question concerning DMol3. I have a system which I optimized using a few constraints (fixing XYZ positions of some atoms) to save computational time, and also because it is supposed to serve as a model for a larger system where some motions will not be possible due to the atomic environment. I then performed a calculation of vibrational properties and thermodynamic properties using DMol3 for the system without fixing any atomic coordinates.

The output tells me that the system has some imaginary frequencies. When I look at the corresponding vibrations, it is obvious that these are mainly movements of those atoms that were not allowed to relax during the optimization. Now, I am wondering whether I can still use the thermodynamic quantities obtained in the calculation (ZPVE, enthalpy at given T)? Or will the presence of imaginary frequencies affect the results to an extent these quantities are no longer valid?

Any comments would be highly appreciated.

Best wishes,

Michael