# [molpro-user] rhf convergence problems

Jose A. Gamez joseantonio.gamez at uam.es
Wed May 12 17:31:47 BST 2010

```Dear all,

I'm trying to perform a CCSD(T) calculation on a radical-anionic molecule.
However, I have great troubles to converge the ROHF calculation (the UHF
converges OK). I've tried a couple of things:

* I've used a smaller basis set (sto-3g and dvz, although the ROHF dvz
calculation didn't converge) RHF calculation as initial guess of my ROHF
calculation.

* I've used the restricted orbitals of the neutral molecule as initial guess.

* I've increased the value of the shift of the open orbitals up to -0.3 .

I think that the origin of this problem is that there is an excited state
lying close to the ground state. But, since I optimised the UHF wavefunction,
I would like to converge the ROHF.

You have any tips?

Thanks a lot for your help.

Cheers,

Jose

P.D. I include the input file if that helps

***, CCSD(T) avtz calculation

!basis=sto-3g

geomtyp=xyz
geometry={
8
Title
Se           0.119746   -0.439567    0.252388
Se           0.214836    0.063065    2.534400
C           1.973623    0.030962   -0.199635
H           2.638913   -0.492006    0.483666
H           2.169261   -0.260569   -1.233496
H           2.091656    1.105526   -0.073333
O           1.479630   -2.438497    2.672993
H           0.982562   -2.250200    1.856981
}

!{rhf;
! wf,charge=-1;
! print,orbitals;
!}

basis=vdz
rhf
{rhf;
shift,-0.3,-0.3;
wf,charge=-1}

basis=avtz
!print,basis

!rhf
{rhf;
wf,charge=-1;
shift,-0.3,-0.3;
! print,orbitals;
}

put,molden,CH3SeSeOH-TSOHan.TZ.molden

pop
{pop;
density,spin}

uccsd(t)
---

--
Jose A. Gamez

Departamento de Química, C-13