Dear users and developers!

I am trying to compute optimum geometry of fused trifuran at the CCSD/aug-cc-pVDZ level of theory, for its ground state, lowest singlet state, kation, anion and the lowest triplet state.

For the cc-pVDZ basis set there are no problems. Adding the diffuse functions to the basis set brings about serious problems for the lowest singlet state and, quite surprisingly, for the ground state.
There is virtually no energy change after a few steps, but the gradient and displacement are still over the convergence thresholds.

I have tightened the convergence criteria for the CC part with no visible improvement. GDIIS also does not help. What else could I try and, more importantly, what may be the reason for such a peculiar behavior?

I am attaching below the input file for the ground and for the excited state optimizations.

I'll be grateful for any help in this matter.

Marcin

ground state:

$molecule
0 1
H 3.8725561106 0.0000000000 0.9595558189
C 2.8958752861 0.0000000000 0.4830501588
C 2.5157976879 0.0000000000 -0.8421444650
H 3.1817159086 0.0000000000 -1.7018350830
C 1.0782273822 0.0000000000 -0.7812826583
C 0.7170052587 0.0000000000 0.5507972281
O 1.8135630184 0.0000000000 1.3572455219
C -0.7170052587 0.0000000000 0.5507972281
C -1.0782273822 0.0000000000 -0.7812826583
O 0.0000000000 0.0000000000 -1.6459401359
C -2.5157976879 0.0000000000 -0.8421444650
C -2.8958752861 0.0000000000 0.4830501588
O -1.8135630184 0.0000000000 1.3572455219
H -3.1817159086 0.0000000000 -1.7018350830
H -3.8725561106 0.0000000000 0.9595558189
$end

$rem
jobtype OPT
CORRELATION CCSD
BASIS aug-cc-pVDZ
SCF_GUESS CORE
SCF_CONVERGENCE 8
CC_CONVERGENCE 9
GEOM_OPT_TOL_GRADIENT 60
GEOM_OPT_MAX_DIIS 5
N_FROZEN_CORE FC
MEM_STATIC 2000
CC_MEMORY 80000
$end

excited:

$molecule
0 1
H 3.8616882412 0.0000000000 0.9619535490
C 2.8825490321 0.0000000000 0.4896042968
C 2.4838325058 0.0000000000 -0.8628651031
H 3.1488621713 0.0000000000 -1.7233658965
C 1.0825174523 0.0000000000 -0.8034856928
C 0.6938039454 0.0000000000 0.5723922013
O 1.7874510834 0.0000000000 1.3842390573
C -0.6938039454 0.0000000000 0.5723922013
C -1.0825174523 0.0000000000 -0.8034856928
O 0.0000000000 0.0000000000 -1.6756215359
C -2.4838325058 0.0000000000 -0.8628651031
C -2.8825490321 0.0000000000 0.4896042968
O -1.7874510834 0.0000000000 1.3842390573
H -3.1488621713 0.0000000000 -1.7233658965
H -3.8616882412 0.0000000000 0.9619535490
$end

$rem
jobtype OPT
CORRELATION CCSD
BASIS aug-cc-pVDZ
SCF_GUESS CORE
SCF_CONVERGENCE 8
CC_CONVERGENCE 12
GEOM_OPT_TOL_GRADIENT 60
EE_STATES [0,0,1,0]
CC_STATE_TO_OPT [3,1]
EOM_DAVIDSON_CONVERGENCE 12 use tighter convergence for EOM amplitudes
CC_T_CONV 12 use tighter convergence for CCSD amplitudes
N_FROZEN_CORE FC
MEM_STATIC 2000
CC_MEMORY 75000
$end