Journal Article relativistic effects electronic structure relativistic basis sets CCFDF/QTAIM model DFT methods DKH2 Gaussian type-orbitals Generator Coordinate Research Support, Non-U.S. Gov't barrier height basis set bidentate dimers computational calculation computational thermochemistry density functionals effective core potential electric field gradients energy analysis hydrogen bond infrared intensities interacting quantum atom nitric oxide donors nuclear quadrupole moments polynomial expansion prolapse free quantum theory of atoms in molecules relativistic transition state variational prolapse