[gmx-users] x2top and bonds. No forcefield type for atom S (2) with 3 bonds

[Vitaly V. Chaban]

Hi,

This can be the reason when X2TOP gives the following error:
"
Fatal error:
No forcefield type for atom S (2) with 3 bonds
"
?

I try to translate PDB of the TFSA anion
       O    O
       ||     ||
F3C-S-N-S-CF3
       ||     ||
       O    O

into topology.


My PDB contains optimized geometry:
HEADER    TFSA
COMPND    TFSA
AUTHOR    VVC
ATOM      1  N   TFS     1      -0.000   0.444  -0.008  1.00  0.00
ATOM      2  S   TFS     1       1.401  -0.440  -0.189  1.00  0.00
ATOM      3  S   TFS     1      -1.400  -0.438   0.189  1.00  0.00
ATOM      4  O   TFS     1      -1.236  -1.810  -0.833  1.00  0.00
ATOM      5  O   TFS     1      -1.284  -1.009   1.805  1.00  0.00
ATOM      6  O   TFS     1       1.293  -1.026  -1.800  1.00  0.00
ATOM      7  O   TFS     1       1.233  -1.803   0.845  1.00  0.00
ATOM      8  C   TFS     1      -2.837   0.628  -0.107  1.00  0.00
ATOM      9  C   TFS     1       2.836   0.630   0.105  1.00  0.00
ATOM     10  F   TFS     1      -3.996  -0.097   0.093  1.00  0.00
ATOM     11  F   TFS     1      -2.805   1.094  -1.408  1.00  0.00
ATOM     12  F   TFS     1      -2.807   1.698   0.766  1.00  0.00
ATOM     13  F   TFS     1       2.802   1.099   1.404  1.00  0.00
ATOM     14  F   TFS     1       2.803   1.698  -0.771  1.00  0.00
ATOM     15  F   TFS     1       3.996  -0.093  -0.093  1.00  0.00
END

and my n2t file is

C   C   1   C               ; CNT Carbon with one bond
C   C   2   C   C           : CNT double bonded Carbon
O   O   1   C               ; CARBONYL OXYGEN (C=O)
O   OM  1   C               ; CARBOXYL OXYGEN (CO-)
O   OA  2   C   H           ; HYDROXYL OXYGEN (OH)
O   OW  2   H   H           ; WATER OXYGEN
N   N   3   H   C   C       ; PEPTIDE NITROGEN (N OR NH)
N   NT  3   H   H   C       ; TERMINAL NITROGEN (NH2)
N   NL  4   C   H   H   H   ; TERMINAL NITROGEN (NH3)
N   NR5 2   C   C           ; AROMATIC N (5-RING,2 BONDS)
N   NR5*    3   C   C   H       ; AROMATIC N (5-RING,3 BONDS)
N   NP  3   C   C   FE      ; PORPHYRIN NITROGEN
C   C       3   C   O   *       ; BARE CARBON (PEPTIDE,C=O,C-N)
; Note that order is importante here because of wildcards.
C   C3  4   H   H   H   *   ; ALIPHATIC CH3 GROUP
C   C2  4   H   H   C   *   ; ALIPHATIC CH2 GROUP
C   C1      4   H   C   *   *   ; ALIPHATIC CH GROUP
C   CB      3   C   C   C       ; BARE CARBON (5-,6-RING)
H   H       1   N               ; HYDROGEN BONDED TO NITROGEN
H   HO      1   O               ; HYDROXYL HYDROGEN
H   HW      1   OW              ; WATER HYDROGEN
H   HS      1   S               ; HYDROGEN BONDED TO SULFUR
H   HC      1   C               ; HYDROGEN BONDED TO CARBON
S   S       4   C  0.181  N  0.167 O 0.172  O  0.172
F   F       1   C



The Sulphur atoms have each 4 bonds but X2TOP wants them to have only
3. If I change the string in the N2T to 3 bonds, the topology is
generated but S-C bond is absent.

What can be the problem?

Thanks.
-- 
Vitaly V. Chaban, Ph.D.
http://www-rmn.univer.kharkov.ua/chaban.html