Hello
I am new to the computational suite"MolPro" and I am trying to do the frequency calculation for a small organic molecule. Following is my Input data:
***, Name frequency calculation
memory,50,m
geomtyp=z-matrix
symmetry,nosym
geometry
basis=6-31+g(d,p);
{rhf;
wf,charge=0,symmetry=3,spin=0;}
$functional=b3lyp3;
{freq,sym=nosym
print}
---
The output data I obtained shows no convergence and following error:
? Error
? No convergence
? The problem occurs in rhfpro
I would be very thankful, if anyone of you could help me to find the cause of this error and how it can be removed.
Regards
Mallika Khare
You can try to first run B3LYP3 in a smaller basis and then let Molpro to start the proper calculation from converged SCF vectors from this smaller basis. There are also options for difficult convergence cases. See Molpro manual and examples for details.
I think you need try with different sets of coordinates for atoms of your molecule. It would be better if you can first optimize your molecule with the help of some classical force field (for e.g. UFF) using AVOGADRO software, which is not a big deal.
Now copy the new set of coordinates from AVOGADRO to molpro. It gives two benefits to you, a) Less convergence/iteration steps in MOLPRO, b) Optimized geometry is the global minima or lying on the near by local minima.
Cheers
From the input example it follows that Mallika just wants to obtain the RHF energy for a given geometry (no OPTG keyword), so changing this geometry is out of question.
Another story is that Mallika assumes that this geometry is already a stationary point, otherwise calculating frequencies (FREQ keyword) makes little sense.
What looks suspicious to me is the line "wf,charge=0,symmetry=3,spin=0". This means you ask for an electronic state other than the totals symmetric A state (which irreducible representation 3 means depends on the point group of your molecule). That means if your molecule has a closed shell singlet configuration symmetry=3 is not the ground state, which could explain the convergence problems.
Try to start with a small basis set and run the calculation again. If you still have the same problem, then I think your starting geometry is not that good. You can also use free software like IQmol or Avogadro to visualize your molecule and then start to minimize the initial structure energy.
Hello all
Thank you very much for your help and responses. I got the solution by changing symmetry=3 to symmetry=0 and introducing number of electrons to my input file.
Thank you all once again for your help.
Regards
Mallika Khare
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