[gmx-users] Membrane protein MD Simulation

[Mark Abraham]

Behnoush Zare wrote:
> Dear Yanzi,
> Thank you for your swift response. I did all you wrote to me. Also I include ffG43a1 forcefield in the lipid.itp file and then include the lipid.itp file in the protein.top at line 12 as forcefield parameter. When I run grompp the following error appeared:

Be careful mixing two force fields unless you know what you are doing, 
i.e. other people have published with this mix. See 
http://wiki.gromacs.org/index.php/Force_Fields#Usage

> Fatal erroe; Invalid order for directive moleculetype, file "protein.top",  line 14
> 
> What is this error and what do I have to do?

This means the directives in the .top file (possibly via an .itp 
#include) are out of order. Directives look like "[ moleculetype ]". See 
chapter five of the GROMACS manual for the order in which they need to 
appear.

Mark