10.5 Visualizing and Plotting Orbitals, Densities, and Other Volumetric Data 10.5.5 Direct Generation of “Cube” Files 10.5.7 Electron Localization Function

10.5.6 Noncovalent Interactions (NCI) Plots

(February 4, 2022)

Weitao Yang and co-workers^{535, 220} 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}}

(10.21)

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 $s(\mathbf{r})$ . 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