7. Property calculation

7.1 Geometric quantities

Taking into account electronic correlation is necessary to determine bond lengths, bond angles and molecular conformations with good accuracy. It should be noted that Hartree-Fock theory can be shown to systematically underestimate bond lengths, when calculations are pushed to the Hartree-Fock limit (full base of atomic orbitals). At present, DFT calculations using a well-chosen functional such as B3LYP and a sufficiently extensive atomic orbital base (e.g. triple zeta plus polarization) generally enable geometric structures to be calculated with an accuracy equivalent to that of X-ray diffraction, particularly for organic molecules. Other hybrid (PBE0, B3PW91,...) or meta-GGA (M06-2X, for example) functions also perform well in this field