ffTK torsion scan convergence using Gaussian.

From: Dipak Balasaheb Sanap (dipakbs_at_udel.edu)
Date: Mon Nov 12 2018 - 18:08:12 CST

Dear all,
I am trying to parameterize an organic molecule using ffTK. Things run
smooth for everything except torsion scan for 1 dihedral. Reading log file
suggest that optimization is not converging, I get the following error in
log file.

Predicted change in Energy=-1.997999D-02
 Optimization stopped.
    -- Number of steps exceeded, NStep= 120
    -- Flag reset to prevent archiving.

After reading few threads on various mailing lists, I did try few things as
follows:

1. Changed the MaxCycles=1000
# opt (modredundant,MaxCycles=1000) MP2/6-31g(d) Geom=PrintInputOrient

2. Tried restart from the existing checkpoint file. Input file for restart
as follows:
%NoSave
%chk=FRA.scan9.pos.chk
%nproc=36
%mem=406GB
#opt (modredundant,Restart,MaxCyc=1000) MP2/6-31g(d) Guess=Read
Geom=Checkpoint

Error for restart:
Restoring state from the checkpoint file "FRA.scan9.pos.chk".
ONIOM results not found on unit 2.

I am, attaching the input file any suggestion would be really useful.
I have also visualized the log file using QM tools, nothing looks broken.

Dipak Sanap
PhD in Chemistry,
University of Delaware.


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