[gmx-users] Again: Non-integer charges in tpr-files

[Erik Lindahl]

Hi,

> But on the other hand: Isn't -2.399999e+01 integer enough? I'm a bit 
> confused here about the limits one should accept for "wrong" charges, 
> because I got those warnings after my first mail (maybe due to a wrong 
> value I posted there (-3.2 instead of -32 (or 31.99999e+1))).
> 
> I could send you my stuff if you still think this is an error (and not 
> just a bunch of protonated sidechains with a roundoff).

Sorry, perhaps I misunderstood you; if you expected a net charge of 24 
in the system, this is perfectly OK.

I actually tried to "fix" this a long time ago, but it isn't trivial; we
are summing a lot of charges, and due to the way they are represented in
hardware they aren't exact. One option would of course be to only warn
when the net charge is more than 0.01% of the system charge RMSD or 
something, but that might hide things like having one charged lipid 
among 1024 uncharged ones... I'll see if we attack it again.

Cheers,

Erik