Dear all,
I am trying to obtain a relaxed scan of furan and some other molecules in the S1 state, using sos-ri-adc(2)/def2-tzvp, and increasing C-O distance. Several of the initial geometries appear to approach conical intersections well documented in the literature. However, a couple of these geometries have a negative S1 excitation energy. How should I interpret this? Is this calculation still reliable?
Here is a fragment of the control file for the ricc2 calculation:
$denconv 0.10000000E-06
$freeze
implicit core= 5 virt= 0
$cbas file=auxbasis
$ricc2
adc(2)
geoopt model=adc(2) state=(a 1)
sos cos= 1.30000
maxiter=60
$excitations
irrep=a multiplicity= 1 nexc= 4 npre= 5 nstart= 6
$closed shells
a 1-18 ( 2 )
Also, some of the output of ricc2.
+==================================================================+
| sym | multi | state | CCS excitation energies |
| | | +--------------------------------------------+
| | | | Hartree | eV | cm-1 |
+==================================================================+
| a | 1 | 1 | 0.0077019 | 0.20958 | 1690.370 |
| a | 1 | 2 | 0.1500643 | 4.08346 | 32935.306 |
| a | 1 | 3 | 0.1510398 | 4.11000 | 33149.398 |
| a | 1 | 4 | 0.2295911 | 6.24749 | 50389.415 |
| a | 1 | 5 | 0.2469002 | 6.71850 | 54188.332 |
+==================================================================+
+================================================================================+
| sym | multi | state | ADC(2) excitation energies | %t1 | %t2 |
| | | +----------------------------------------+--------+--------+
| | | | Hartree | eV | cm-1 | % | % |
+================================================================================+
| a | 1 | 1 | -0.0086017 | -0.23406 | -1887.848 | 89.97 | 10.03 |
| a | 1 | 2 | 0.0606178 | 1.64949 | 13304.069 | 82.25 | 17.75 |
| a | 1 | 3 | 0.1137216 | 3.09452 | 24959.007 | 90.70 | 9.30 |
| a | 1 | 4 | 0.1630437 | 4.43665 | 35783.961 | 87.32 | 12.68 |
+================================================================================+
Thanks in advance for any help,
Daniel.