Hi, All,

Following some posts to the forum about computing IR intensities, I wrote a script to do this.

This script generates a hessian file to compute approximate IR intensities for periodic structures with DMol3. The atomic polar tensors (i.e., the dipole terms) necessary for  intensities are approximated by computing Hirshfeld charges for each atom and then evaluating the dipole moment using these charges. These derivatative dipoles are stored in a study table along with the Cartesian derivatives needed for computing IR frequencies.

Once you generate the hessian file you will need to use Tools | Vibrational Analysis to complete the evaluation of the frequencies and intensities.

This method was originally published by Prof. Timothy Korter's research group in Allis, et al., J. Phys. Chem. A (2006) 110, 1951-1959. Keep in mind that this produces only an approximation to the actual atomic polar tensors, but the Allis paper demonstrates that this isn't a bad approximation, at least for the types of molecular crystals that they study.  I'd really appreciate feedback from people on how well this approximation works for the systems that you are modeling.

Best regards,

George

ps. The script is attached, along with an example application to glycine crystal. That's in MS 5.5 format, so you might have trouble opening the structure and study table with early versions on MS.