Stability_analysis

Questions
#1

Hi All,
I was trying to analyze wavefunction stability of biradicaloids, but getting this, please suggest what to do now ?
Output file data:
Stability analysis will be performed

Iter Rts Conv Rts Left Ttl Dev Max Dev

1 0 2 0.000529 0.000264
2 0 2 0.000155 0.000107
3 0 2 0.000053 0.000041
4 0 2 0.000026 0.000022
5 1 1 0.000014 0.000013
6 1 1 0.000005 0.000004
7 1 1 0.000003 0.000002
8 2 0 0.000001 0.000001 Roots Converged
RHF-> UHF unstable, 1 negative eigenvalue(s): -0.0560132

Triplets done: starting singlet calculation

Iter Rts Conv Rts Left Ttl Dev Max Dev

9 0 2 0.000656 0.000328
10 0 2 0.000205 0.000147
11 0 2 0.000092 0.000064
12 0 2 0.000034 0.000023
13 0 2 0.000014 0.000011
14 1 1 0.000006 0.000005
15 1 1 0.000003 0.000002
16 1 1 0.000002 0.000001
17 2 0 0.000001 0.000001 Roots Converged
RHF-> RHF stable, smallest eigenvalue: 0.0861101
RHF->CRHF stable, smallest eigenvalue: 0.0915771

SETman timing summary (seconds)
CPU time 1047.51s
System time 0.00s
Wall time 356.22s

Thankyou

#2

Congratulations, you are the proud owner of a triplet instability. Means that unrestricting (UHF) will lower the energy. Not altogether surprising for a biradical. A fully variational solution will require UHF. Will result in a lower energy at the expense of sacrificing spin symmetry (<S^2>).

#3

Thankyou for the details it means alot.

#4

By the way, Q-Chem’s internal stability analysis codde perturbs the MO coeffs in the direction of energy lowering and leaves them on disk, so that you can use SCF_GUESS=READ in a subsequent job to try to find the lower-energy SCF solution.