AMBER: antechamber - improper torsions

From: Oliver Hucke <>
Date: Tue, 20 Jul 2004 09:23:02 -0700

Dear All,

I am using antechamber for the preparation of the amber input files for
various small molecules. I noticed that for many sp2 atoms no improper
torsions are present neither in gaff.dat nor in the frcmod file obtained
with parmchk. Leap does not complain but I can find several warnings
like the following in the leap.log file when I load these molecules:

No sp2 improper torsion term for c2-ha-c2-c3
No sp2 improper torsion term for ca-ha-ca-ca

Can I ignore these warnings or should I add impropers for each sp2 atom?
I was thinking of using the following entry in parm99.dat as a template:

X -X -CA-HA 1.1 180.0 2.

I would appreciate very much your comments on this!

Thanks a lot,


Oliver Hucke, Dr.
                               Health Sciences Building - K418C
University of Washington      1959 NE Pacific St.
Dept. of Biochemistry         phone: (206) 685 7046
Box 357742                    fax  : (206) 685 7002
Seattle, WA 98195-7742        email:
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Received on Tue Jul 20 2004 - 17:53:01 PDT
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