Electron density distributions in hydrogen bonds: A local density-functional study of α-oxalic acid dihydrate and comparison with experiment

Accurate local density-functional calculations of the electron density distribution in α-oxalic acid dihydrate, C2H2O4⋅2H2O, are performed and compared with experimental densities obtained from high-resolution x-ray diffraction measurements at 100 K. Results are corrected for basis set superposition errors. The agreement between the vibrationally averaged theoretical and experimental density improves significantly when taking into account the effects of hydrogen bonding and crystal environment. Electron density redistributions due to strong hydrogen bonds are found to outweigh the experimental standard deviation only in the bond region of the molecules involved as donor of the hydrogen bond.