10.5 Visualizing and Plotting Orbitals, Densities, and Other Volumetric Data

10.5.5 Noncovalent Interactions (NCI) Plots

Weitao Yang and co-workers444, 178 have shown that the reduced density gradient,

s(𝐫)=(12(3π2)1/3)^ρ(𝐫)ρ(𝐫)4/3 (10.17)

provides a convenient indicator of noncovalent interactions, which are characterized by large density gradients in regions of space where the density itself is small, leading to very large values of s(𝐫). Q-Chem can generate noncovalent interactions (NCI) plots of the function s(𝐫) in three-dimensional space. To generate these, set the PLOT_REDUCED_DENSITY_GRAD $rem variable to TRUE. (See the nci-c8h14.in input example in $QC/samples directory.)