DIP-EOM-CCSD

Singlet-triplet separations of di-radicals treated by the DEA/DIP-EOM-CCSD methods... 

We first observe that, for both the DIP-STEOM-CCSD and DIP-EOM-CCSD results, the relative ionization potentials are very consistent between the... 

The relative IPs are also found to agree very well between the DIP-STEOM-CCSD md DIP-EOM-CCSD methods. The largest deviation is found for the two high-lying states of E symmetry. The lower of the two E states shows appreciable dependence on the basis set and differs by 0.4 eV between the DIP-SITEOM and DIP-EOM results. It is likely that the close proximity of two states of the same symmetry causes this higher sensitivity. Nevertheless, for nearly all of the states, the agreement is excellent. 

NOs Ground State, Dsh w DIP-STEOM-CCSD DZP T72P DIP-EOM-CCSD DZP TZ2P ... 

As seen previously, the vertical DIP-STEOM-CCSD calculations find the E" state to be very close in energy to the E" state (see Table II). This result is supported by the DIP-EOM-CCSD calculations as well. We again note the discrepancy with the DFT calculations of Wang (5) and the MCSTEP results of Heryadi (7). These other results may be questioned, however, as previously discussed. We are left with the suggestion that the E" state contributes to the lower-energy peaks in the region of 13.18 eV observed in the PE spectrum (see Figure 2). 

In contrast to the E" 1L2S minimum in DIP-STEOM-CCSD, a recent DFT study (14) reported a significantly distorted 1S2L structure for the E" state (Ri=1.152 A R2=R3=1.315 A Ai2=Ai3=132°). It is unclear if the stationary point was verified to be a true minimum by vibrational frequency calculations. As an additional confirmation of the DIP-STEOM-CCSD results, we also performed DIP-EOM-CCSD geometry optimizations and vibrational frequency calculations on the E" state. The DIP-EOM method finds C2v minimum and transition state structures nearly identical to the DIP-STEOM results in Table VII. 

The NO3 vertical ionization spectrum was calculated by the DIP-STEOM-CCSD and DIP-EOM-CCSD methods. These methods avoid artifactual symmetry breaking of the reference wavefunction by starting from the symmetry-correct nitrate anion orbitals and provide a balanced treatment of dynamical and non-dynamical correlation effects. In general, the DIP-STEOM and DIP-EOM results agree well with the experiment of Wang (5) and with previous theoretical assignments (5,7). However, in our calculations, the vertical transition to the E" state nearly coincides with that of the E" state, in contrast to previous studies. Our calculations therefore do not support the assignment of the broad experimental feature near 14.05 eV to the E" state. 

---