[gmx-users] Problem force constant bond stretc.

[Paolo Costa]

Dear Gromacs users,

I have a problem regarding force constant for bond stretching. By employing
VFFDT software, I got C-C bond stretching force constant (for Benzene,
B3LYP-6311++G*) equal to 383.23 kcal/ (mol A^2) which is equivalent to
160343 kj/ (mol nm^2). However when I look to the ffbonded.itp file of
Amber99.ff the CA-CA force constant value is 392459.2  kj/ (mol nm^2). It
seems that the value I got from VFFDT is somehow half than the one reported
in Amber force field.
Can somebody help me to figure out such issue?

Thanks a lot in advance for your help.
-- 
Paolo Costa, Ph.D.
Postdoctoral Researcher
Department of Chemistry and Biomolecular Sciences
University of Ottawa
10 Marie Curie, Ottawa, ON K1N 6N5, Canada
Room number: DRO 326 (D'Iorio Hall)