[CP2K:4388] amber torsion energy

Teodoro Laino teodor... at gmail.com
Mon Apr 22 16:53:03 UTC 2013

Dear Letif,

thanks for reporting this issue. All parameters should be converted at the moment they are read. We also had few examples to check the numerics and I remember they were matching with Sander they were OK.
Do you have an input file (including all relevant files) that shows this problem?


On Apr 22, 2013, at 5:23 PM, Letif Mones <letif... at gmail.com> wrote:

> Hi,
> I did a molecular mechanical calculation in cp2k using an amber topology file (force field: amber99). When I checked the bonded energy terms I found that the bond and angle terms are correct but the dihedral energy is twice as the energy calculated by sander. I think the reason is that in the amber FF the form of the torsion potential is: K / 2 * [ 1 + cos[ M*PHI - PHI0 ] ] while cp2k uses the form of  K * [ 1 + cos[ M*PHI - PHI0 ] ].
> So should not the torsion force constant read from an amber topology file be multiplied by 0.5 (and the improper one too as it has the same form)?
> Letif
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