CHARMM Development Project Forums CHARMM Community Bug Reports & Fixes GEO Dihedral does not work with 'SYMMETRIC'

Hi All,
This is a bug report based on my use of version c33b2, I apologize if this has been corrected in later versions - I don't currently have access to a later version.

In the CHARMM MMFP documentation it states that the 'symmetric' keyword can be used in conjunction with a GEO dihedral restraint. My testing of this indicates this is not the case.

For example, this restraint will NOT produce a flat bottom potential between +/- 10 degrees of the target dihedral angle of 90 degrees:

set tref = 90.0
MMFP
GEO MAXGEO 200 sphere RCM dihedral iummfp 10 -
harmonic symmetric force 100.0 TREF @tref DTOFF 10 -
select segid main .and. resid 1 end -
select segid main .and. resid 2 end -
select segid main .and. resid 3 end -
select segid main .and. resid 4 end
END

However, as stated in test case c30test/mmfp_test5.inp two GEO calls, with the 'OUTSIDE' and 'INSIDE' keywords invoked can be used to achieve this.

set tref = 90.0
MMFP
GEO MAXGEO 200 sphere RCM dihedral iummfp 10 -
harmonic INSI force 100.0 TREF @tref DTOFF 10 -
select segid main .and. resid 1 end -
select segid main .and. resid 2 end -
select segid main .and. resid 3 end -
select segid main .and. resid 4 end
GEO sphere RCM dihedral -
harmonic OUTS force 100.0 TREF @tref DTOFF 10 -
select segid main .and. resid 1 end -
select segid main .and. resid 2 end -
select segid main .and. resid 3 end -
select segid main .and. resid 4 end
END

At a minimum the CHARMM MMFP documentation should probably be corrected to note this (see Example #9 of the Examples Section of mmfp.doc).

Ed