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

10.5.6 Noncovalent Interactions (NCI) Plots

(December 20, 2021)

Weitao Yang and co-workers 535 Johnson E. R. et al.
J. Am. Chem. Soc.
(2010), 132, pp. 6498.
, 220 Contreras-García J. et al.
J. Chem. Theory Comput.
(2011), 7, pp. 625.
have shown that the reduced density gradient,

s(𝐫)=(12(3π2)1/3)^ρ(𝐫)ρ(𝐫)4/3 (10.21)

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.)