[gmx-users] X's in the ffcharmm27bon.itp force field

[Mark Abraham]

On 2/04/2010 4:50 AM, Lum Nforbi wrote:
> Hello all,
>
>    Please, can someone let me know why there are X's in the
> [dihedraltypes] section of the ffcharmm27bon.itp force field and what
> they actually stand for? Could they be replaced with actual atoms or no?
> I appreciate your replies.

That's a CHARMM feature - they're a "wildcard" atom to which any type 
can match.

Mark