Example: Asymptotically correct XC potentials: CO¶
For property calculations, xc potentials with asymptotically correct (-1/r) behavior outside the molecule, the results tend to be superior to regular LDA or GGA calculations. This is especially true for small molecules and for properties that depend heavily on the proper description of the outer region of the molecule. In the example, all-electron basis sets are used. This is mandatory for the SAOP potential.
In the first example, excitation energies are calculated with the GRACLB potential. This potential requires one number as argument: the experimental ionization potential in atomic units. This number can be either based on an experimental value, or on previous GGA total energy calculations.
$ADFBIN/adf <<EOR title CO excitations grac potential BeckeGrid Quality good End XC Model GRACLB 0.515 End Atoms O 0 0 0 C 1.128205364 0 0 end Excitation Lowest 10 Onlysing End Basis Type TZ2P Core None End end input EOR rm TAPE21 logfile
The same calculation with the SAOP xc potential would differ in the XC block only:
XC Model SAOP End
SAOP depends on the orbitals which makes it more expensive to evaluate than GRAC for large molecules, but is much easier to use, since it does not require an ionization potential parameter as input.