First mp2 6-311+G** optimization of its geometry has an imaginary frequency around 170cm-1, but B3lyp optimization has none.
Second, Prof. Truhlar and his group's pair-density gives the first one more than 3 eV, using Aldet, 10 active orbitals and RHF 6-31+G* moread vecs, with C1 symmetry. A camb3lyp calculation can almost repeat the results in literature using the jaggon A' for n-pi and A" for pi-pi*(ref. _Nonadiabatic Absorption Spectra and Ultrafast Dynamics of DNA and RNA Photoexcited Nucleobases, where there is no S4 for B3lyp).
GAMESS camb3lyp
...
STATE ENERGY EXCITATION TRANSITION DIPOLE, A.U. OSCILLATOR
0 -> HARTREE EV X Y Z STRENGTH
0 A' -414.7069620565 0.000
1 A'' -414.5213813410 5.050 0.0000 -0.0000 0.0028 0.0000
2 A' -414.5097188475 5.367 1.0631 -0.4247 -0.0000 0.1723
3 A'' -414.4861385240 6.009 -0.0000 0.0000 -0.1483 0.0032
4 A'' -414.4753929241 6.301 -0.0000 -0.0000 -0.0053 0.0000
5 A' -414.4677738792 6.509 -0.4857 0.0161 -0.0000 0.0377
...
Cs symmetry of uracil with cr-eomccsd(t) has been calculated, but eomccsd give the symmetry order A', A", A",A',A',A'....
SYMMETRY ENERGY (H) ENERGY (EV) ENERGY (H) ITERATIONS
A'' 0.19066910 5.188 -413.61129095 CONVERGED
A' 0.20396370 5.550 -413.59799636 CONVERGED
A'' 0.22028254 5.994 -413.58167752 CONVERGED
A' 0.24516544 6.671 -413.55679462 CONVERGED
A'' 0.25588124 6.963 -413.54607882 CONVERGED
A'' 0.25681275 6.988 -413.54514730 CONVERGED
....
delta cr-eomcc(2,3),B can give the closest value when compared with experimental value, apparently.
First mp2 6-311+G** optimization of its geometry has an imaginary frequency around 170cm-1, but B3lyp optimization has none.
Second, Prof. Truhlar and his group's pair-density gives the first one more than 3 eV, using Aldet, 10 active orbitals and RHF 6-31+G* moread vecs, with C1 symmetry. A camb3lyp calculation can almost repeat the results in literature using the jaggon A' for n-pi and A" for pi-pi*(ref. _Nonadiabatic Absorption Spectra and Ultrafast Dynamics of DNA and RNA Photoexcited Nucleobases, where there is no S4 for B3lyp).
GAMESS camb3lyp ...
STATE ENERGY EXCITATION TRANSITION DIPOLE, A.U. OSCILLATOR 0 -> HARTREE EV X Y Z STRENGTH 0 A' -414.7069620565 0.000 1 A'' -414.5213813410 5.050 0.0000 -0.0000 0.0028 0.0000 2 A' -414.5097188475 5.367 1.0631 -0.4247 -0.0000 0.1723 3 A'' -414.4861385240 6.009 -0.0000 0.0000 -0.1483 0.0032 4 A'' -414.4753929241 6.301 -0.0000 -0.0000 -0.0053 0.0000 5 A' -414.4677738792 6.509 -0.4857 0.0161 -0.0000 0.0377 ...
Cs symmetry of uracil with cr-eomccsd(t) has been calculated, but eomccsd give the symmetry order A', A", A",A',A',A'....
SYMMETRY ENERGY (H) ENERGY (EV) ENERGY (H) ITERATIONS A'' 0.19066910 5.188 -413.61129095 CONVERGED A' 0.20396370 5.550 -413.59799636 CONVERGED A'' 0.22028254 5.994 -413.58167752 CONVERGED A' 0.24516544 6.671 -413.55679462 CONVERGED A'' 0.25588124 6.963 -413.54607882 CONVERGED A'' 0.25681275 6.988 -413.54514730 CONVERGED .... delta cr-eomcc(2,3),B can give the closest value when compared with experimental value, apparently.
Very Best Regards!