[gmx-users] Problem force constant bond stretc.

[David van der Spoel]

Den 2020-04-15 kl. 23:48, skrev 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.
> 
Vbond = (k/2) (r - r0)^2

Some methods do not use the division by two, so it can be a matter of 
definition.

-- 
David van der Spoel, Ph.D.,
Professor of Biology
Uppsala University.
http://virtualchemistry.org