14-scaling

[Ewald Pauwels]

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?

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.

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.

Thanks in advance for any comments,
Ewald.