Hi all

recently I started to engage in QM calculation of protein-ligand complex

As expected protein-ligand complex is too big to do QM calculation.

So, I tried to reproduce the procedure in following paper

Zhang, D. W., and J. Z. H. Zhang. 2003. Molecular fractionation with

conjugate caps for full quantum mechanical calculation of proteinmolecule interaction energy. J. Chem. Phys. 119:3599–360

In this paper. They split protein to each amino acid fragment with suitable N-terminal and C-terminal cap which mimics the original electrostatic environment of protein.

and each amino acid fragment was used as an input to Gaussian calculation.

So I made an amino acid fragment of my protein as written in this paper and I run the Gaussian with one of the fragments with counterpoise = 2( my object is to calculate interaction energy between protein and ligand)

But I got the following error

SCF Error SCF Error SCF Error SCF Error SCF Error SCF Error SCF Error SCF Error

ERROR!!!!

SCF has not converged. Gradients and post-SCF results would be GARBAGE!!

SCF Error SCF Error SCF Error SCF Error SCF Error SCF Error SCF Error SCF Error

The attached gz file is the folder that has amino acid fragment file and one of Gaussian input file(

5dadA_TX6_frag_131.com( original fragment pdb is 5dadA_TX6_frag_131.pdb) and its result log( 5dadA_TX6_frag_131.out)

and the other attached file is the paper about MFCC( above paper)

Actually, it's my first time starting with QM subject. so maybe I could miss some basics in QM field.

Any kind of comment or suggestion would be really appreciated.

Thanks

Regards

Jong hui