Table 2. Singlet–triplet energy gap (kcal mol–1) for CAS(2,2) active space a .
| Acene | CASSCF |
CASPT2 |
tPBE (CAS-PDFT) |
Literature values
b
|
||||
| Vert. | Ad. | Vert. | Ad. | Vert. | Ad. | Vert. c | Ad. d | |
| Naphthalene | 86.4 | 72.2 | 77.0 | 68.2 | 74.5 | 66.4 | 76.0 | 64.4 |
| Anthracene | 61.2 | 50.2 | 60.1 | 51.9 | 59.6 | 51.8 | 56.8 | 46.2 |
| Tetracene | 46.5 | 37.5 | 40.8 | 34.4 | 37.2 | 31.8 | 40.4 | 34.1 |
| Pentacene | 37.7 | 29.6 | 34.2 | 28.5 | 31.3 | 26.4 | 31.3 | 24.3 |
| Hexacene | 25.3 | 19.4 | 23.6 | 19.9 | 19.7 | 16.8 | 22.8 | 18.7 |
| Heptacene | 18.5 | 15.3 | 18.5 | 17.4 | 14.2 | 13.6 | 18.1 | 13.9 |
| Octacene | 10.0 | 7.7 | 14.0 | 13.6 | 9.6 | 9.7 | 13.4 | 11.5 |
| Nonacene | 8.8 | 6.4 | 11.3 | 11.5 | 5.8 | 6.6 | 10.7 | 10.4 |
| Decacene | 4.7 | 2.0 | 10.2 | 10.4 | 5.4 | 6.1 | 8.1 | 9.0 |
| Undecacene | 4.8 | 1.3 | 8.4 | 8.8 | 2.0 | 3.3 | 7.1 | 9.4 |
| Dodecacene | 2.8 | –1.6 | 8.7 | 9.1 | 3.5 | 4.6 | NA e | 8.9 |
| MUD f | 4.1 | 5.1 | 1.3 | 2.2 | 3.1 | 3.0 | ||
aGeometries are optimized using B3LYP/6-31G(d,p) level of theory (with broken-symmetry solutions). CASSCF, CASPT2, and tPBE calculations are performed using the 6-31+G(d,p) basis set.
bHighest-level available literature estimates.
cCCSD(T)/cc-pV∞Z from ref. 21.
dAverage adiabatic gaps from Table 1.
eNot available.
fMean unsigned deviation from highest-level available literature estimates.