Hello,
I would like to compute several excited states of imidazole at the CASCI level using the DETCI module. However, I found the energy of the fifth singlet A’ root is different from that obtained from MOLPRO, PYSCF, and FORTE. Here are the lowest ten singlet roots from PSI4 and PYSCF:
PSI4 FORTE PYSCF
0 -224.691712103656 -224.691712104509 -224.691712094605
1 -224.429346130922 -224.429346135865 -224.429346112673
2 -224.390513013585 -224.390513011981 -224.390512997860
3 -224.320978021557 -224.320978022408 -224.320977987456
4 -224.295459370323 -224.292448261076 -224.292448213622
5 -224.292448260642 -224.246878466006 -224.246878429002
6 -224.246878464020 -224.182666735126 -224.182666705548
7 -224.182666735803 -224.160425516424 -224.160425517110
8 -224.160425514624 -224.138610351221 -224.138610346631
9 -224.138610351305 -224.089241000935 -224.115300786446
It seems that the fifth state is an “extra” singlet state. It turns out that this state is a sextet as found by PYSCF (E = -224.295459326146 E(CI) = -12.2576489903539 S^2 = 5.9999998
).
Here is the Psi4 input I use.
molecule imidazole {
0 1
H 0.000000 2.119822 0.714354
H 0.000000 1.202262 -1.904898
H 0.000000 -2.104815 0.663782
H 0.000000 -0.010302 2.116597
C 0.000000 1.120107 0.305897
C 0.000000 0.635508 -0.983749
C 0.000000 -1.091835 0.283881
N 0.000000 -0.741378 -0.994001
N 0.000000 0.000000 1.104571
}
set {
reference rhf
scf_type pk
basis def2-svp
e_convergence 10
d_convergence 8
maxiter 100
docc [15,3]
restricted_docc [14,0]
active [1,6]
reference_sym 0
num_roots 10
}
Ecas, wfn = energy('detci', return_wfn=True)