I’m using RI-ADC(2) to compute the excitation energies of an organic molecule. However, I’m finding that the same state is printed twice. E.g.:
--------------------------------------------------------------------------------
Excited state 1 (triplet, A) [converged]
----------------------------------------------------------------------------
Term symbol: 1 (3) A R^2 = 3.52560e-09
Total energy: -1906.6089668619 a.u.
Excitation energy: 1.146602 eV
V1^2 = 1.0000
Important amplitudes:
occ i occ j vir a vir b v
-----------------------------------------------------------
113 (A) A 114 (A) A 0.6993
113 (A) A 119 (A) A 0.0519
-----------------------------------------------------------
----------------------------------------------------------------------------
Excited state 2 (triplet, A) [converged]
----------------------------------------------------------------------------
Term symbol: 2 (3) A R^2 = 8.93858e-09
Total energy: -1906.6089667826 a.u.
Excitation energy: 1.146605 eV
V1^2 = 1.0000
Important amplitudes:
occ i occ j vir a vir b v
-----------------------------------------------------------
113 (A) A 114 (A) A 0.6993
113 (A) A 119 (A) A 0.0520
-----------------------------------------------------------
The two states printed have the same energy and show the same amplitudes for the same orbital. This does not match experiment or other Ab-initio calculations.
Is this a bug, or am I missing something about the ADC calculation?
Here’s my job control input:
$rem
BASIS = cc-pVDZ
MAX_SCF_CYCLES = 150
AUX_BASIS = rimp2-cc-pVDZ
EE_SINGLETS = 5
EE_TRIPLETS = 5
MEM_TOTAL = 34000
MEM_STATIC = 4000
METHOD = ADC(2)
adc_do_diis = true
ADC_DAVIDSON_MAXSUBSPACE = 100
ADC_DAVIDSON_MAXITER = 500
integrals_buffer = 200
PRINT_ORBITALS true
MOLDEN_FORMAT true
$end