The analytic second derivatives were implemented for general coupled cluster and configuration interaction methods. These procedures made possible the highly accurate calculations of second order properties. The effect of higher excitation on harmonic vibrational frequencies and nuclear magnetic resonance (NMR) chemical shifts was also studied. The large impact of higher excitations on vibrational frequencies was revealed. It was found that for NMR shifts, the CCSD(T) method overestimates higher order effects and provides better results than CCSDT.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry