Spectrum calculation and assignment#

Take your favorite (small) molecule:

  • Perform structure optimization

  • Calculate the valence spectra using:

    • TDHF

    • TDDFT

      • BLYP

      • B3LYP

      • BHandHLYP

    • ADC

      • ADC(1)

      • ADC(2)

      • ADC(3)

  • Plot and compare the spectra

    • Which methods agree/disagree?

    • How does the absolute energy of BLYP - B3LYP - BHandHLYP - TDHF look?

      • Compare to HOMO-LUMO gaps

    • TDHF and ADC(1) [or CIS] should be almost identical - verify this

  • Analyse and assign the features (using the ADC(3) results)

Cost-saving measures#

Looking at water with ADC(2) and a reasonably large basis set, investigate the influence of cost-saving measures, such as:

  • Freezing the core-orbital

  • Freezing a percentage of the highest-energy virtuals

  • Freezing virtuals according to the restricted virtual space protocol discussed here

How are the spectra affected? What are the computational savings? How does it change when using ADC(2) instead of ADC(3)?