[gmx-users] Use dihedraltype 4 to allow several multiplicity terms

[Steven Neumann]

Dear Gmx Users,

I used charmm server to get the parameters for my new molecule -
alkane. i converted it into the gromacs topology.
When I try grompp:

WARNING 1 [file ffbonded.itp, line 7948]:
  Overriding Proper Dih. parameters.
  Use dihedraltype 4 to allow several multiplicity terms.

  old: 0 0.159787 2 0 0.159787 2
  new: CG331      CG321      CG321      CG331      9          0.00
  0.1598288  2


WARNING 2 [file ffbonded.itp, line 7949]:
  Overriding Proper Dih. parameters.
  Use dihedraltype 4 to allow several multiplicity terms.

  old: 0 0.159829 2 0 0.159829 2
  new: CG331      CG321      CG321      CG331      9          180.00
  0.1330512  6

My ffnonbonded.itp corresponding lines:

[ dihedraltypes ]
; i	j	k	l	func	phi0	cp	mult
CG331      CG321      CG321      CG331      9          0.00
0.1598288  2
CG331      CG321      CG321      CG331      9          180.00     0.1330512  6

Can you please explain me this? Shall use 4 instead of 2 or 6 at the
end of these lines?
I am using Gromacs 4.5.5

Stevem