--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test-data/oplsaa.ff-tip4p.itp	Tue Dec 21 13:42:46 2021 +0000
@@ -0,0 +1,52 @@
+;
+; Note the strange order of atoms to make it faster in gromacs.
+;
+[ moleculetype ]
+; molname	nrexcl
+SOL		2
+
+[ atoms ]
+; id	at type	res nr 	residu name	at name	cg nr	charge
+1       opls_113        1       SOL      OW     1       0.0
+2       opls_114        1       SOL     HW1     1       0.52
+3       opls_114        1       SOL     HW2     1       0.52
+4       opls_115        1       SOL      MW     1      -1.04
+
+#ifndef FLEXIBLE
+[ settles ]
+; OW    funct   doh        dhh
+1       1       0.09572    0.15139
+#else
+[ bonds ]
+; i	j	funct	length	force.c.
+1	2	1	0.09572	502416.0 0.09572	502416.0 
+1	3	1	0.09572	502416.0 0.09572	502416.0 
+	
+[ angles ]
+; i	j	k	funct	angle	force.c.
+2	1	3	1	104.52	628.02	104.52	628.02	
+#endif
+
+[ exclusions ]
+1	2	3	4
+2	1	3	4
+3	1	2	4
+4	1	2	3
+
+; The position of the virtual site is computed as follows:
+;
+;		O
+;  	      
+;	    	D
+;	  
+;	H		H
+;
+; const = distance (OD) / [ cos (angle(DOH)) 	* distance (OH) ]
+;	  0.015 nm	/ [ cos (52.26 deg)	* 0.09572 nm	]
+
+; Vsite pos x4 = x1 + a*(x2-x1) + b*(x3-x1)
+
+[ virtual_sites3 ]
+; Vsite from			funct	a		b
+4	1	2	3	1	0.128012065	0.128012065
+