*From*: "Adam Langlois" <Adam.Langlois|-|USherbrooke.ca>*Subject*: CCL:G: DFT Methods For Intermolecular Pi-Pi Interactions*Date*: Thu, 22 Nov 2012 10:48:40 -0500

Sent to CCL by: "Adam Langlois" [Adam.Langlois||USherbrooke.ca] I have been assigned a calculations project where I am asked to do a DFT calculations to optimise the geometry of a porphyrin triamer and hexamer that interact through Pi-Pi interactions with C60. The interaction is a "ball-in- glove" type of interaction where there is an overlap of the Pi orbitals of the porphyrin rings and the Pi orbitals of the C60. My question is what DFT method is best suited for this type of calculation? For most of the calculations that I have carried out in the past I have used the B3LYP method. However, I have heard that this is not the best method for long-distance or intermolecular interactions. I have been told about two other methods that may be useful in a situation like this. The first is the CAM-B3LYP method which is supposed to take long distance interactions into account. However, I have recently compared the CAM-B3LYP method to the B3LYP method in calculations that involved a co- facial special pair of porphyrin and found that the B3LYP method better represented that experimental data. I have also heard of the a method known as the M05-2X functional, which is supposed to another good method for long distance interactions such as hydrogen bonding. However, I do not see this functional as an option in the Gaussian calculation set-up window. A second question is with regard to the basis sets. I plan on using the ONIOM method to save on computation time. I plan on applying the PM6 method as a low level and a DFT method as a high level. However I am not sure how large of a basis set I should use. Normally I carry out my calculations with a 6-31G* basis set. Is this large enough to take into account the intermolecular interactions or go I need to employ a more disperse basis set such as 6-311g++. A paper that I found used a 6-311g++(2df,2dp) basis set to examine intermolecular hydrogen bonding which is a large, and very disperse basis set. However, the paper also modelled very small structures. Any suggestions for basis sets here would be appreciated. Finally, once I have modelled the triamer and the hexamer without C60 I will need to model them with C60. Where again I will employ the ONIOM method. My question here is, do I include the C60 in my high layer or my low layer? I would like to thank you in advance for all of your help. Adam Langlois Universite de Sherbooke Quebec Canada Adam.Langlois*o*USherbrooke.ca