[gmx-users] a huge topology parameter c1 (angles)

[Mark Abraham]

Egidijus Kuprusevicius wrote:
> Dear users,
> 
> from PRODRG beta server I have got a very big c1 parameter in my 
> topology file is that normal or smth is wrong with my topology?
> 
>  
> 
> [ angles ]
> 
> ; ai aj ak fu c0, c1, ...
> 
> ....
> 
> 17 19 21 2 120.0 505.0 120.0 505.0 ; CAH CAD CAP
> 
> 20 19 21 2 120.0 505.0 120.0 505.0 ; HAD CAD CAP
> 
> 19 21 22 2 120.0 560.0 120.0 560.0 ; CAD CAP CAC
> 
> 19 21 24 2 120.0 560.0 120.0 560.0 ; CAD CAP CAE
> 
> 22 21 24 2 120.0 *560.0* 120.0 *560.0* ; CAC CAP CAE
> 
> 21 22 23 2 180.0 *41840001.2* 180.0 *41840001.2 ;* CAP CAC NAB
> 
> 21 24 25 2 120.0 *505.0* 120.0 *505.0 ;* CAP CAE HAE
> 
> 21 24 26 2 120.0 505.0 120.0 505.0 ; CAP CAE CAI
> 
> 25 24 26 2 120.0 505.0 120.0 505.0 ; HAE CAE CAI
> 
> 16 26 24 2 120.0 505.0 120.0 505.0 ; CAR CAI CAE

You'll notice that this angle is linear - angle 180 degrees. (If you 
don't know how to read these lines, consult the table in Chapter 5 of 
the manual.) A large force constant would prevent any deviation from 
linear, which I can imagine is right for some weirder chemical species.

Mark