Dear CP2K users, I am trying to do a run using a flexible version of a 4-site water model. I am trying to use the &CONSTRAINT module to describe a virtual atom (MW) as a function of the O-H distances but I do not want the whole water molecule treated as a rigid body. I have specified the virtual atom constraint using the &VIRTUAL_SITE definition but I have commented other constraints regarding the water molecule. However, I am unable to make it work. Could you please have a look at it and let me know what I am doing wrong or whether it is possible or not? Thanks very much for any help, Carlos I have attached the input files and below is the error I get ********************************************************* *** ERROR in get_molecule (MODULE molecule_types_new) *** ********************************************************* *** The pointer lci is not associated *** *** Program stopped at line number 279 of MODULE molecule_types_new *** ===== Routine Calling Stack ===== 3 velocity_verlet 2 qs_mol_dyn_low 1 CP2K