Independent Gradient Model Plot
Initially developed for promolecular
electron density (ED, xyz input file), the new IGM approach
derives from the NCI approach
developed in 2010 by W. Yang et al., and has been extended to relaxed ED calculated from a wave function
(wfn input file)
An extremely appealing feature of the IGM approach is the opportunity to monitor separately selected bonds. It paves the way for the targeted mechanistic exploration of reactions.
is a free open-source program developed to identify molecular interactions and prepare data to build 2D and 3D representations of them in the molecular environment. IGMPlot enables NCI calculations as well.
It can be downloaded
As an alternative, to help handling IGMPlot calculations in a very easy and straightforward way,
without installing/compiling the source code, an IGMPLot on-line portal has been designed by Dr Arnaud
Renard (http://www.arnaudrenard.com). Its name is “IGMPlot on-demand”
and it is hosted on the
romeolab web server: https://romeolab.univ-reims.fr
(one of the ROMEO computational center activities).
Please follow the procedure described in the documentation to create and activate your account.
The 'IGM' model relies on a virtual upper limit of the ED gradient representing a non-interacting system. This reference enables quantifying the net drops observed in NCI plots. A new descriptor has been derived: δg. It is the difference between ∇ρIGM
and the true ED gradient ∇ρ: it can be seen as a measure of electron sharing brought by ED contragradience. An attractive feature of the new IGM methodology is to provide an uncoupling scheme that automatically extracts the signature of intermolecular interactions (δginter
) for drawing the corresponding 3D iso-surface representations in real space with software like VMD for instance.
The user no longer needs to choose an arbitrary promolecular ED fraction threshold as proposed in NCI plot to differentiate grid points associated to intermolecular situations from other (undesired) points corresponding to intramolecular regions. Using QM ED, it is no longer necessary to choose appropriate ED cutoffs in a way that produces well-separated strong/weak interaction domains. The program is able to filter weak intramolecular interactions (H-bond and ring closure interactions) from the data without any specific manipulation in the input parameters. The IGM reference gives a unique definition of the interaction region: each point of the δg 2D plot corresponds solely to interaction situations. As a consequence, the IGM approach overcomes difficulties to define NCI regions within integration procedures.
: please feel free to report errors, omissions, corrections in IGMPlot code or in the supporting documentation.
: a GPU accelerated version of NCI (cuNCI) has been written by our group and can downloaded here