Hi all,

I have recently been investigating the differences between forcefields for minimising organic crystal structures, and have hit upon an oddity. 

When I minimise an experimental crystal structure, certain forcefields will give me totally unphysical energies (positive lattice energies).  This is sometimes improved by the use of an improved electrostatic model (but not always) and even then, I find that the electrostatic contribution is not really that believeable.  I attach the calculation set up I was using - it should import as 'test'.

If anyone has had any similar experiences, or insight into why this is happening, it would be much appreciated.