Electron Densities of Several Small Molecules As Calculated from Density Functional Theory

The electron densities of CH3F, CO, CO2, H2CO, H2O, HCN, HF, and NH3 have been calculated by density functional theory (DFT) methods with various exchange and correlation functionals and are compared with QCISD (quadratic configuration interaction method including single and double substitutions) results. The DFT methods yield electron densities and Laplacians of the densities in good agreement with the QCISD results. As expected, the gradient-corrected functionals including B3LYP, B3P86, BP86, and BLYP improve the densities calculated by the local spin density approximation relative to the corresponding QCISD densities. Relative to his 1988 functional, Becke's three-parameter exchange functional clearly improves the results for equilibrium geometries, vibrational frequencies, dipole moments, and electron densities. For all gradient-corrected functionals, the results are generally insensitive to the numerical accuracy of the grid. The basis set, however, has a significant effect on the electron density, w...