I am working with protein which has Tryptophan (TRP) and Histidine (HSD) residues at some position. Both the residues are suppose to have neutral charge. However when I checked the structure of my protein, both residues shows slight net positive charge 1.110223E-16. I checked partial charges on the atoms and it exactly matches with partial charges given in RTF file. I get this value of slight positive charge when I do "scalar charge stat/show sele resid @residuenumber end"

I was confused as why would these residues show me charge like this when partial charges matches that shown in RTF file?

regards,
Adi

Is 1.11E-16 a large number?

No at all and I would not worry about it much. But I was just wondering why should it not be 0?

Not all floating point numbers can have an exact binary representation, so in the general case there will inevitably be a roundoff error.

Thanks,