[gmx-users] failed to make rtab.xvg (arithmetic exception)

[Lianqing Zheng]

Dear Gromacs pals:

When I was trying to simulate a SiO2 system with Buckingham potential and
Coulomb potential, the program got an arithmetic exception error during
the process of making tables for the potentials before any step begins.
Here are the last several lines in the .log file. I'm confused that it
says no routines for table, but it was actualling making tables. I checked
the example of water in tutor directory, no problem with it at all. Then I
tried to water.mdp for my simulation, but it didn't solve the problem.
I'll attach my .top at the end of this email and hopefully you may find
some defects in it which cause the problem.

<---------------log------------------------->
Table routines are used for coulomb: FALSE
Table routines are used for vdw:     FALSE
Cut-off's:   NS: 0.85   Coulomb: 0.85   BHAM: 0.85
Determining largest Buckingham b parameter for table
Buckingham b parameters, min: 0, max: 48.7318
Generated table with 500 data points for COUL.
Tabscale = 500 points/nm
Generated table with 500 data points for LJ6.
Tabscale = 500 points/nm
<---------------log------------------------->

Comparing water and SiO2, I found that in my case only ctab.xvg and
dtab.xvg were produced while water has one more file: rtab.xvg. So there
may be some problem with the repulsive part of potential, which is
Aexp(-b*r) in Buckingham. I printed out tablescale in init_table() in
table.c and here are the results:

tabscale=1082081280
tabscale=1082081280
tabscale=0

Then the arithmetic exception happened. 

---------------.top------------------------------
[ defaults ]
2 1 no 1.0 1.0

[ atomtypes ]
;name        mass      charge   ptype            c6           c12
   SI    28.08000        2.40        A   	0.0 0.0 0.0
    O    15.99940       -1.20        A   	0.0 0.0 0.0

[ nonbond_params ]
  ; i    j func           a             b	c6
    O    O    2 1.339973E+5	     27.6	1.688507E-2
    O	SI    2 1.737112E+6	  48.7318	1.288457E-2
   SI	SI    2		0.0	      0.0	0.0

[ moleculetype ]
SI 0

[ atoms ]
1	SI	1	SI	SI	2	2.4	28.08000

[ moleculetype ]
O 0

[ atoms ]
1	O	1	O	O	1	-1.2	15.99940

[ system ]
Silica SiO2

[ molecules ]
SI 512
O 1024
----------------end of my top-----------------------------------

I'd greatly appreciate your help! I've been stuck here for quite a while.

Lianqing