Multiwfn forum

prasanta13

Member

Registered: 2018-12-30

Posts: 39

AIM analysis

Dear Prof Tian Lu and/or other members
I am trying to investigate the Non-Covalent interaction between radical (CH3) and halogen bond donors. I find three very close/dense NCI isosurfaces which are red/blue (weak v d w interaction), so i started to use AIM to search for 3,-1 bcps. The BCPs do not reflect the proper interaction sites as observed from the NCI analysis.
Out of the three NCI surfaces, I find two 3,-1 bcp and one 3,+1 rcp. I do not know if the RCP is attractive or repulsive contribution. The bond path is also wrong. The poincare-hopf relationship also do not hold.
what to do?

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,640

Website

Re: AIM analysis

1 Probably the initial guessing points are not appropriate, please try other modes in main function 2 for searching CPs
2 Presence RDG isosurface doesn't necessarily mean that there is a corresponding BCP, see J. Chem. Theory Comput., 9, 3263 (2013) for relevant discussion.
You can gradually decrease isovalue of RDG to check if a CP exists within the RDG isosurface. If the CP indeed exists, the RDG isosurface will not disappear until the isovalue is very close to 0 (implying that there is a point with vanishing electron density gradient). Some discussions about this trick is given in http://sobereva.com/267 (written in Chinese, but you can use Google translator)