[gmx-users] Pdb for urea crystal

[Dallas B. Warren]

> I tried with 8 molecules . But it shows the following error, 
> Invalid order for directive moleculetype, file 
> ""/usr/local/gromacs/share/gromacs/top/spc.itp"", line 1 

Try searching the emailing list for that error.  I don't recall the
specifics, but it means that you have some line repeated in one of your
topology files (.itp or .top), which you have to removed.  This issue
comes up when there are multiple .itp files called and both of them
contain the same line.