Independent gradient model based on Hirshfeld partition: A new method for visual study of interactions in chemical systems

Abstract

The powerful independent gradient model (IGM) method has been increasingly popular in visual analysis of intramolecular and intermolecular interactions in recent years. However, we frequently observed that there is an evident shortcoming of IGM map in graphically studying weak interactions, that is its isosurfaces are usually too bulgy; in these cases, not only the graphical effect is poor, but also the color on some areas on the isosurfaces is inappropriate and may lead to erroneous analysis conclusions. In addition, the IGM method was originally proposed based on promolecular density, which is quite crude and does not take actual electronic structure into account. In this article, we propose an improvement version of IGM, namely IGM based on Hirshfeld partition of molecular density (IGMH), which replaces the free-state atomic densities involved in the IGM method with the atomic densities derived by Hirshfeld partition of actual molecular electron density. This change makes IGM have more rigorous physical background. A large number of application examples in this article, including molecular and periodic systems, weak and chemical bond interactions, fullydemonstrate the important value of IGMH in intuitively understanding interactions in chemical systems. Comparisons also showed that the IGMH usually has markedly better graphical effect than IGM and overcomes known problems in IGM. Currently IGMH analysis has been supported in our wavefunction analysis code Multiwfn (http://sobereva.com/multiwfn). We hope that IGMH will become a new useful method among chemists for exploring interactions in wide variety of chemical systems.

Intermolecular Vibration Energy Transfer Process in Two CL-20-Based Cocrystals Theoretically Revealed by Two-Dimensional Infrared Spectra

“…Therefore, we used the IGMH method to analyze intermolecular non-covalent interactions in TNT/CL-20 and HMX/CL-20, where the atomic densities were derived by Hirshfeld partitioning of the actual molecular electron density. [ 41 , 42 ] Figure 5 illustrates the intermolecular non-covalent interaction between TNTs and CL-20 and between HMX and CL-20s. Figure 5 (left) shows that there is mainly a vdW interaction between CL-20 and in TNTs, which has the largest non-covalent interaction isosurface, such as the interaction between N 1 O 2 and N 12 O 2 .…”

“…In this work, we theoretically investigate the intermolecular vibration energy transfer processes in TNT/CL-20 using 2D IR spectra. At the same time, the non-covalent intermolecular interaction and the stability of the trigger bond N-NO 2 are studied using the independent gradient model based on the Hirshfeld partition (IGMH) method [ 42 , 43 ] and the Mayer Bond Order Density (BOD) method [ 44 ], respectively. For comparison, the above characteristics of HMX/CL-20 are also investigated.…”

Two Novel Co-Crystals of Naproxen: Comparison of Stability, Solubility and Intermolecular Interaction

“…The interaction energies of NPX–CPL and NPX–OMT were calculated at m062x -D3/jun-cc-pvtz level using counterpoise corrections method [ 50 ]. In addition, the intermolecular interactions existing in the co-crystals NPX–CPL and NPX–OMT were explored by independent gradient model based on Hirshfeld partition (IGMH) method using Multiwfn program [ 51 , 52 ]. The lattice energy calculations were performed for the co-crystals NPX–CPL and NPX–OMT using CRYSTAL17 at the B3LYP level of DFT using the 6-31G (d, p) basis set [ 53 ].…”

Novel dual-motor nanorotator assembled by cyclo[18]carbon and figure-eight carbon hoop

“…The independent gradient model based on Hirshfeld partition (IGMH) is a very intuitive method proposed by one of us to graphically depict the main interaction regions between specific fragments of compounds by using the isosurface of δg inter function. [48] The two C 18 rings and the OPP unit in 2C 18 @OPP are respectively defined as fragments for calculation. The fairly extended δg inter isosurface in green color between C 18 and OPP indicates that the interaction between host and guest molecules covers a very wide spatial region (Figure 4(c)) and the electron density on it is very small of about 0.005 a.u.…”