TJ Mustard wrote:


I started a small 2 nucleic acid system for FEP testing. As well as turning on fep, I set RNA_Chain_A as the couple-moltype. I also set couple-lambda0 and couple-lambda1 to vdw-q and none respectively. I then began a "steep" mdrun and got this error:


Unrelated to your error, but potentially problematic: decoupling both LJ and Coulombic interactions simultaneously might lead to convergence problems. See the free energy tutorial for information.


Program mdrun, VERSION 4.5
Source code file: topsort.c, line: 112

Fatal error:
Function type Improper Dih. not implemented in ip_pert
For more information and tips for troubleshooting, please check the GROMACS
website at http://www.gromacs.org/Documentation/Errors

I have searched for this on google and found nothing. Do I need an Improper Dihedral section in my top/itp file? I have ran this same

If you have planar compounds (like nucleic acids), you likely have a [dihedrals] directive that corresponds to the impropers. Check the function types.

system with fep off and it runs perfectly.


It looks like the code in topsort.c does not deal with both F_IDIH and F_PIDIH, which maybe (?) is the source of the problem. Normal harmonic impropers can be perturbed, i.e.:

    case F_IDIHS:
        bPert = (ip->harmonic.rA  != ip->harmonic.rB ||
                 ip->harmonic.krA != ip->harmonic.krB);
        break;

Perhaps there's something about your impropers that doesn't allow for perturbation. At the very least, a test for F_PIDIH is missing, but I'll defer to the developers to weigh in on the need for a fix.

-Justin


Any help is much appreciated.

TJ Mustard
Email: musta...@onid.orst.edu


--
========================================

Justin A. Lemkul
Ph.D. Candidate
ICTAS Doctoral Scholar
MILES-IGERT Trainee
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin

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