Concerning the level of theory, Crawford et al. [55] concluded
that TD-DFT exhibits the cotton pole at higher wavelengths in the
case of diffuse, Rydberg states when compared with CCSD calculation.
Applying the mpw1pw91/cc-pvdz level of theory, the
calculated ORD values of limonene at four wavelengths matched
very well to the experimental values obtained in solution, with
relative differences smaller than 5%, and absolute deviations
smaller than 5. In addition, previous work on a minor conformer of
strychnine indicated that the mpw1pw91/cc-pvdz level of theory is
superior to the “working horse” of geometry optimization, i.e.
B3LYP/6-31G(d) [17].