Molcas Forum

moabe

Member

Registered: 2018-06-03

Posts: 23

CASSCF Geometry Optimization

Hi Everyone,

I want to do relaxed potential energy scan for a ring-opening reaction (bond breaking) in ground and first singlet excited states using CASSCF(10,10)/cc-pVDZ level of theory. To do so, I've decided to do a constrained geometry optimization for each points along the PES. I used DFT optimized structure as initial structure for the CASSCF calculations. For many points, the geometry did not converge. I tried to restart the calculation from the last structure but it also did not work. Does anyone have any solution for this issue? Thanks.

Note: 10 electron in 10 orbitals obtained from some test calculations for vertical excitation energy at FC point and compared to experimental value.

I use Molcas 8 and this is my input:   

&Gateway
RICD 
coord=MyStructure.xyz
Basis=cc-pVDZ
Group=C1
Constraint
  a  =  Bond  C5  C10
  Value
  a  =  1.57759 angstrom
End  of  Constraints

>>>  Do  while

&SEWARD
&GRID_IT
All; ASCII 
&RasScf
Spin=1; Nactel= 10 0 0; Inactive= 42; Ras2= 10
Rlxroot=  1 
&SLAPAF

>>>  EndDo

Best,

Mostafa

Ignacio

Administrator

From: Uppsala

Registered: 2015-11-03

Posts: 1,085

Re: CASSCF Geometry Optimization

Hard to know if there's any solution without knowing what goes wrong. It could be the active space is not stable (I presume you included at least the sigma and sigma* orbitals of the bond being breaking), it may be beneficial to do some state averaging (CIRoot keyword).