[CP2K:4390] amber torsion energy

[Letif Mones]

Hi Teo,

I am sending the following files: amber and cp2k inputs, amber restart file and amber topology file (dmpoh_vacuum.atop). I also attached another topology file (dmpoh_vacuum_mod.atop) in which I halved the dihedral force constants. With this latter cp2k gives the right answer.

Regards,

Letif

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On 22 Apr 2013, at 17:53, Teodoro Laino wrote:

> 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?
> 
> Thanks,
> Teo
> 
> 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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