Dear all, some time ago, I posted a query on the qm/mm methods but since i managed to solve it, i did not return to the forum. my apologies and thank you to people who followed the question. I am posting for another error that I am getting. I am trying to run a qm/mm on a protein-ligand system. I have successfully done classical MD without errors. i used a well equilibrated .rst file from the classical MM method and was able to do further equilibration with qm/mm using the PM3 Hamiltonian. It is in the MD production phase. 

I want to repeat the same with SCC-DFTB but unfortunately it keeps giving errors in the equilibration phase such as

QMMM SCC-DFTB: !!!! ============= WARNING ============= !!!!

QMMM SCC-DFTB: Convergence could not be achieved in this step.

QMMM SCC-DFTB: The calculation will continue, but energies and

QMMM SCC-DFTB: forces for this step will not be accurate.

or the vlimit exceeded if I use dftb_telec=100 after 200 steps. I have looked around on the AMBER mailing list and know its a common error. I also tried using the PM3 equilibrated file and trying to further equilibrate it with the SCC-DFTB. But the error still remains. I am attaching my input file. I am sure someone has done it and resolved the issue. Could they share their experience?

thanks