[gmx-users] BKS potential SiO2 again

[gmx at 4ka.mipt.ru]

> Did your atoms have initial velocities? From my experience (T>100K), it
> takes much more just 200 step to get equilibrated. Have you tried to let
> your system (btw: how many atoms?) run for 50ps or longer?

I use boxes with different sizes
 from 1125 to 9000 atoms. Result everytime the same.
System always has sharp pick at 1.7A for Si-O bond length,as
shown here
http://4ka.mipt.ru/rdf.xvg.
 ^^^It is after 100ps at 1K.

It is good, but.. I'm absolutly sure, that with BKS potential
it is possible to obtain 1.62 A for Si-O bond.
My aq.top:

[ defaults ]
; non-bond type  combination rule
2 1
[ atomtypes ]
;name        mass      charge   ptype       A            B         C6
 O    15.99940        0.0        A      0.0          0.0       0.0
 SI    28.08000        0.0        A      0.0          0.0       0.0

[ nonbond_params ]
; i    j func           a             b       c6
O  O    2 1.339973E+5          27.6       1.688480E-2
SI  O    2 1.737084E+6       48.7318       1.288436E-2
SI SI    2         0.0           0.0       0.0
[ moleculetype ]
; name nrexcl
SI     0
[ atoms ]
; nr   type   resnr  residue   atom   cgnr   charge      mass
1     SI     1     SI    SI    1       2.4     28.08000
[ moleculetype ]
; name nrexcl
O     0
[ atoms ]
; nr   type   resnr  residue   atom   cgnr   charge      mass
1      O     1      O     O    2       -1.2    15.99940
[ system ]
 Silica
[ molecules ]
O        750
SI       375









> Lianqing
>
>
> On Wed, 2 Jun 2004 gmx at 4ka.mipt.ru wrote:
>
> >
> >Hello.
> >Im trying to simulate SiO2 at T -> 0 with BKS potential .
> >Starting with a-quartz-like structured box at 1K with
> >R(Si-O)=1.61A after 200 steps i have  box with R(Si-O) = 1.71A.
> >But it must be ~1.61!
> >I know, not long ago there were mistakes in GROMACS code
> >around BKS potential, and I'm not sure, it was solved completly...
> >http://www.gromacs.org/pipermail/gmx-users/2004-January/008952.html
> >Maybe not all bugs were fixed in GMX code?
> >Now I cant obtain beter results, then 1.71 for SI-O distance
> >in any simulation not only near T=0, but in melting/crystallization
> >simulations too with any parameters sets.
> >                                        Lala
> >
> >
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