[gmx-users] Problems with the Dihedral of the Ethanol

[Eudes Fileti]

Dear gmx users
I have attemped to simulate a box of ethanol in normal conditions of
temperature and pressure.
I reproduced very well some literature data (as g(r)) however I had problems
to reproduce the angular
distribution function for the dihedral (C-C-O-H).
This angle must have a peak in 180 degrees and two lesser (and symmetrical)
peaks in 60 and 300 degrees (as shows the figure 1 of this link
http://cbio.mskcc.org/~leonor/jpcb97.pdf ).
However my distribution presents a maximum in 100 degrees with two (but not
symmetrical) peaks the left.
I already made almost everything:
I used both, dihedral GROMACS and Ryckaert-Bellemans, I applied almost all
the avaliables parameters
(eg in ffoplsaabon.itp), I set nrexcl 2, 3, 4, 5, I remade the simulation
several times in with differents conditions, but always I found the same
pattern.
Somebody already had some experience like that? If it had, could you give me
a insight? Bellow I give my top file.
Thank you in advance.
eef

;
;    File 'etanol.top' was generated
;    By user: fileti (1000)
;    On host: linux
;    At date: Sat Jul 15 16:41:25 2006
;
;    This is your topology file
;    "Out Of Register Space (Ugh)" (Vi)
;
; Include forcefield parameters
#include "ffoplsaa.itp"

[ moleculetype ]
; Name            nrexcl
ETH                 2

[ atoms ]
;   nr       type  resnr residue  atom   cgnr     charge       mass
typeB    chargeB      massB
     1   opls_135      1   EtOH     CB      1      -0.18     12.011   ; qtot
-0.18
     2   opls_140      1   EtOH    HB1      1       0.06      1.008   ; qtot
-0.12
     3   opls_140      1   EtOH    HB2      1       0.06      1.008   ; qtot
-0.06
     4   opls_140      1   EtOH    HB3      1       0.06      1.008   ; qtot
0
     5   opls_157      1   EtOH     CA      2      0.145     12.011   ; qtot
0.145
     6   opls_140      1   EtOH    HA1      2       0.06      1.008   ; qtot
0.205
     7   opls_140      1   EtOH    HA2      2       0.06      1.008   ; qtot
0.265
     8   opls_154      1   EtOH     OH      2     -0.683    15.9994   ; qtot
-0.418
     9   opls_155      1   EtOH     HO      2      0.418      1.008   ; qtot
0

[ bonds ]
;  ai    aj funct             c0       c1
    1     2     1          0.10800   284512.0
    1     3     1          0.10800   284512.0
    1     4     1          0.10800   284512.0
    1     5     1          0.14040   392459.2
    5     6     1          0.10800   307105.6
    5     7     1          0.10800   307105.6
    5     8     1          0.13640   376560.0
    8     9     1          0.09450   462750.4

[ angles ]
;  ai    aj    ak funct            c0        c1
    2     1     3     1         107.800    276.144
    2     1     4     1         107.800    276.144
    2     1     5     1         107.800    276.144
    3     1     4     1         107.800    276.144
    3     1     5     1         110.700    313.800
    4     1     5     1         110.700    313.800
    1     5     6     1         109.500    292.880
    1     5     7     1         109.500    292.880
    1     5     8     1         109.500    418.400
    6     5     7     1         107.800    276.144
    6     5     8     1         115.000    334.720
    7     5     8     1         108.000    585.760
    5     8     9     1         109.000    292.880

[ dihedrals ]
;  ai    aj    ak    al funct            c0        c1        c2
c3        c4        c5
    2     1     5     6     3         1.67360  -1.67360   0.00000   0.00000
0.00000   0.00000
    2     1     5     7     3         1.67360  -1.67360   0.00000   0.00000
0.00000   0.00000
    2     1     5     8     3         0.97905   2.93716   0.00000  -3.91622
0.00000   0.00000
    3     1     5     6     3         1.67360  -1.67360   0.00000   0.00000
0.00000   0.00000
    3     1     5     7     3         1.67360  -1.67360   0.00000   0.00000
0.00000   0.00000
    3     1     5     8     3         0.97905   2.93716   0.00000  -3.91622
0.00000   0.00000
    4     1     5     6     3         1.67360  -1.67360   0.00000   0.00000
0.00000   0.00000
    4     1     5     7     3         1.67360  -1.67360   0.00000   0.00000
0.00000   0.00000
    4     1     5     8     3         0.97905   2.93716   0.00000  -3.91622
0.00000   0.00000
    1     5     8     9     3        26.15000  -3.13800 -23.01200   0.00000
0.00000   0.00000
    6     5     8     9     3         0.94140   2.82420   0.00000  -3.76560
0.00000   0.00000
    7     5     8     9     3         0.94140   2.82420   0.00000  -3.76560
0.00000   0.00000


______________________________________
                                      Eudes Eterno Fileti
          Centro de Ciência Naturais e Humanas
                        Universidade Federal do ABC
                                  Rua Santa Adélia, 166
                                            CEP 09210-170
                                               skype: eefileti
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