14-scaling

[Axel]

On Nov 2, 8:31 pm, Ewald Pauwels <ewald.... at ugent.be> wrote:
> Dear all,
>
> Looking into the cp2k input reference, I noticed that the EI_SCALE14
> is standard set to zero. In several of the Fist regtests (e.g. 4:
> nh3_bfgs.inp) this setting is not altered, although the CHARMM
> forcefield is used. Yet, if I have correctly understood the charmm
> documentation, this setting should be 1.0 instead. Am I missing
> something here, or is this setting in the regtests wrong?
dear ewald,

for NH3 the 1-4 scaling is irrelevant.

> On another note, the EI_SCALE14 factor is set to 0.5 for gromos-type
> forcefields in several of the regtests (e.g. 8: G96_ei_scale.inp). I
> don't really understand why this setting would be required. Would
> someone be willing to point out a reference in which that would be
> documented? I can't seem to find a clue in literature.

please note that this example uses a gromos _format_ input,
but the actual forcefield is different (OPLS/AA, if i remember
correctly).
this is probably the general key to your confusion. with cp2k you can
read almost any forcefield parameter set in any of the supported
formats (charmm, gromos, internal cp2k, and soon also amber).

> BTW, I am aware that the regtests are merely there for internal
> checking, but they are the first thing people will start to experiment
> with. If indeed the EI_SCALE14 setting is wrong for the CHARMM
> forcefield, it would be worthwhile to mention it somewhere - f.i. in
> the Google group in response to my question.

what we'd rather need is a proper tutorial, with proper input
examples for typical uses of cp2k. ...or just a collection of "good"
example inputs with a few comments to begin with. any takers?

cheers,
    axel.

> Thanks in advance for any comments,
> Ewald.