CHARMM Development Project Forums User Discussion & Questions Parameter Set Discussion dihedral scan for fused ring system

I am trying to scan one of the dihedrals for the molecule pravastatin using gaussian, as the cgenff output for the dihedral produced a high penalty factor (HGA4 CG2DC2 CG311 CG311 0.2000 3 0.00 ! /tmp/php , from HGA4 CG2DC1 CG321 OG3R60, penalty= 52.7). This dihedral corresponds to H40-C16-C11-C9 (the atoms are part of the fused ring system, attached picture). (P.S. the starting geometry of pravastatin for the dihedral scan was obtained from MP2/6-31g* geometry optimization. There are also other cgenff dihedrals with high penalty factors, and all the atoms in these dihedrals are part of the two fused rings in pravastatin.)

My input file looks like this,

%chk=UNK.scan3.neg.chk

%nproc=32

%mem=32GB

# opt=modredundant MP2/6-31g(d) Geom=PrintInputOrient maxdisk=80gb



UNK Dihedral Scan at MP2/6-31G*



-1 1

O1 2.1570000648498535 0.8140000104904175 0.050999999046325684

O2 6.295000076293945 0.03099999949336052 -0.38999998569488525

O3 -2.6540000438690186 -2.691999912261963 -1.9279999732971191

O4 1.7630000114440918 2.316999912261963 -1.6180000305175781

O5 -3.390000104904175 1.2769999504089355 -1.4019999504089355

O6 -4.408999919891357 3.242000102996826 -0.057999998331069946

O7 -6.201000213623047 2.8580000400543213 1.2970000505447388

.
.
H63 -0.9940000176429749 1.8049999475479126 -0.2619999945163727

H64 -2.046999931335449 2.921999931335449 0.5799999833106995

H65 -0.9399999976158142 1.8949999809265137 1.5130000114440918



D 40 16 11 9 S 18 -10.000000


However, I have been getting error messages that looks like this,

RedQX1 iteration 20 Try 4 RMS(Cart)= 0.00000140 RMS(Int)= 0.15778790 XScale= 2.23810848

RedQX1 iteration 20 Try 5 RMS(Cart)= 0.00000262 RMS(Int)= 0.15778862 XScale= 2.23806748

RedQX1 iteration 20 Try 6 RMS(Cart)= 0.00000229 RMS(Int)= 0.15778929 XScale= 2.23803126

Old curvilinear step not converged, using linear step:

SCX= 1.21D+00 DXMaxT= 6.67D-01 SCLim= 3.33D-01 Fact= 2.77D-01

Error imposing constraints

Error termination via Lnk1e in /opt/software/gaussian/g16.c01/l103.exe at Wed Feb 3 07:52:45 2021.

Job cpu time: 34 days 14 hours 49 minutes 11.0 seconds.

Elapsed time: 1 days 2 hours 4 minutes 7.1 seconds.

File lengths (MBytes): RWF= 54456 Int= 0 D2E= 0 Chk= 51 Scr= 1


I am wondering if you may have suggestions on how I could eliminate this problem. Thanks!