10.5 Visualizing and Plotting Volumetric Quantities 10.5.5 Direct Generation of “Cube” Files 10.5.7 Electron Localization Function

10.5.6 Noncovalent Interactions (NCI) Plots

(September 23, 2025)

Weitao Yang and co-workers ⁶³³ Johnson E. R. et al.
J. Am. Chem. Soc.
(2010), 132, pp. 6498. Link ^, ²⁵⁸ Contreras-García J. et al.
J. Chem. Theory Comput.
(2011), 7, pp. 625. Link have shown that the reduced density gradient,

s(\mathbf{r})=\left(\frac{1}{2(3\pi^{2})^{1/3}}\right)\frac{\|\hat{\bm{\nabla}% }\rho(\mathbf{r})\|}{\rho(\mathbf{r})^{4/3}}

(10.37)

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 $s(\mathbf{r})$ . Q-Chem can generate noncovalent interactions (NCI) plots of the function $s(\mathbf{r})$ 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.)

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10.5.6 Noncovalent Interactions (NCI) Plots