Multiwfn forum

shenaya

Member

Registered: 2019-10-16

Posts: 34

convergence problems in Restricted open shell calculation

Dear All,

I'm performing optimization and frequency calculation on the below system.
It gives a convergence issue.

I have tried several options
ex: increasing the number of cycles.
As we can not use qc, I have used alternative keywords; use=l506

Nothing worked. Your suggestions will be helpful.
Thanks and regards
Shen

opt=calcfc rocam-b3lyp/6-31g(d) scrf=(iefpcm,solvent=water)
scf=maxcycles=125 iop(5/13=1)

Title Card Required

1 2
C 1.35656100 1.13118500 -0.07295400
H 1.28256500 2.07700700 -0.11348300
C 0.90312800 -0.99348200 -0.18842500
H 0.44545800 -1.81385500 -0.32705900
N 0.35868700 0.24094300 -0.38379100
N -4.53096900 0.01670200 0.10290700
H -3.92323500 0.41587700 -0.42267400
H -5.30860900 -0.19732300 -0.32006000
H -4.70348900 0.60048000 0.77614600
H -4.14393200 -0.74142100 0.41322600
N 2.42986200 0.46674300 0.28898400
N 2.14143500 -0.89110000 0.21506800

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,773

Website

Re: convergence problems in Restricted open shell calculation

Do not use ROKS, it is much more difficult to converge than UKS

Never use iop(5/13=1)

scf=maxcycles=125 is meaningless, since it is too close to the default 128

I don't find any reason to use CAM-B3LYP for this system.

I have a blog article to comprehensively discuss how to solve SCF unconvergence problem://www.umsyar.com/61

Try these keywords instead:
# opt B3LYP/6-31g(d) em=gd3bj scrf