Table 1.
Comparison of methods: vertical singlet excited state energies (ΔE) in eV and oscillator strength (f) of G–C base pair calculated with EOM-CCSD(T), CC2/TZVP, ωb97x/6-31G(3df,p), M05-2x/6-31G(3df,p) and ωb97xd/6-31G(3df,p) in the gas phase. Charge transfer (CT) transitions are shown in bold.
| Guanine (G)-Cytosine (C) base pair | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| State | CC2/TZVPa | EOM-CCSD(T)b | ωb97x/6-31G(3df,p) | M05-2x/6-31G(3df,p) | ωb97xd/6-31G(3df,p) | |||||
| Transition | ΔE (f) | Transition | ΔE (f) | Transition | ΔE (f) | Transition | ΔE (f) | Transition | ΔE (f) | |
| S1 | G(π)→G(π)* | 4.88 (0.061) | G(π)→G(π)* | 4.85 (0.07) | G(π)→G(π)* | 5.19 (0.0666) |
G(π)→C(π)* (CT) |
5.06 (0.0411) | G(π)→G(π)* | 5.04 (0.0682) |
| S2 | C(π)→C(π)* | 5.06 (0.063) | C(π)→C(π)* | 4.92 (0.10) | C(π)→C(π)* | 5.32 (0.1753) | C(π)→C(π)* | 5.31 (0.1738) | C(π)→C(π)* | 5.20 (0.1523) |
| S3 |
G(π)→C(π)* (CT) |
5.23 (0.028) |
G(π)→C(π)* (CT) |
5.36 (0.01) | G(π)→G(π)* | 5.82 (0.4531) | G(π)→C(π)* G(π)→G(π)* |
5.32 (0.0347) |
G(π)→C(π)* (CT) |
5.53 (0.0038) |
| S4 | C(n)→C(π)* | 5.49 (0.001) | G(π)→G(π)* | 5.48 (0.41) | GC(n)→C(π)* G(n)→G(π)* |
5.94 (0.0011) | G(π)→G(π)* | 5.74 (0.4392) | G(π)→G(π)* | 5.62 (0.3981) |
| S5 | C(π)→C(π)* | 5.50 (0.183) | C(n)→C(π)* | 5.65 (0.00) | GC(n)→C(π)* G(n)→G(π)* |
6.02 (0.0000) | G(n)→G(π)* | 5.79 (0.0007) | C(n)→C(π)* G(n)→C(π)* |
5.73 (0.0010) |
| S6 | G(π)→G(π)* | 5.51 (0.425) | G(n)→G(π)* | 5.76 (0.00) | GC(π)→C(π)* | 6.09 (0.1232) | C(n)→C(π)* | 5.89 (0.0004) | GC(π)→C(π)* | 5.83 (0.0956) |
| S7 | C(n)→C(π)* | 5.80 (0.000) |
G(π)→C(π)* (CT) |
6.27 (0.0020) | GC(π)→C(π)* | 6.04 (0.0967) | G(n)→G(π)* | 5.90 (0.0001) | ||
| S8 | G(n)→G(π)* | 5.90 (0.000) | G(n)→G(π)* | 6.54 (0.0022) | G(n)→G(π)* | 6.35 (0.0019) | G(n)→G(π)* | 6.32 (0.0014) | ||
| S9 | C(n)→C(π)* | 6.60 (0.0001) | GC(n)→C(π)* | 6.41 (0.0000) | C(n)→C(π)* | 6.50 (0.0000) | ||||