dihedral parameter for conjugated double bonds in GAFF

From: Giulio Rastelli <rastelli.giulio_at_unimo.it>
Date: Wed 14 Aug 2002 03:37:50 -0500

Dear all,

I noticed that the dihedral parameter X -c2-cd-X in gaff.dat has a PK
value of 4.0. If I am correct,
this dihedral should correspond to a double bond and *not* to a single
bond, therefore a value of
26.6 should be set. X -cd-cd-X, which correspond to the inner single
bond, is correctly set to 4.
In parm99, X-CM-CD-X, which correspond to X-c2-cd-X in gaff, was in fact
set to 26.6.
This discrepancy leads to a rather easy rotation of the double bond
during MD, using gaff.
Sorry if this problem has already been reported before, or if I am not

Giulio Rastelli
Dipartimento di Scienze Farmaceutiche
Universita di Modena e Reggio Emilia
Via Campi 183
41100 Modena - ITALY
tel 0039-059-2055145
fax 0039-059-2055131
Received on Wed Aug 14 2002 - 01:37:50 PDT
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