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Figure 3
Electron densities as calculated with VASP (full lines) and QE (dashed lines) along the C—O (top) and C—N (bottom) internuclear axes in the urea crystal. Different DFAs are color coded: LDA in purple, PBE in green and PW91 in black. PW91 QE calculations did not converge with the specified default parameters. Distances are measured from the left nucleus of each pair. The wiggles along the CO line are an artifact from an insufficiently fine default FFT mesh (see the main text). As shown in the insets, where only LDA data are shown (see the main text for details), this pathology is solved using a finer mesh.

IUCrJ
Volume 12| Part 3| May 2025|
ISSN: 2052-2525
https://doi.org/10.1107/S2052252525001721