[gmx-users] PME/Ewald

[David van der Spoel]

On Fri, 19 Oct 2001, Andrew Horsfield wrote:

>I am trying to use something other than the cutoff for electrostatics. The
>key facts of the simulation are:
>
>1) CG relaxation
>2) Net charge on unit cell (-12)
>3) 5805 atoms (including solvent)
>4) I am using PC running Linux (2.4 kernel, RH 7.1)
>
>And I observe:
>
>a) Ewald causes a core dump.
>b) PME give the following output:
>>   Starting Energy   = -5.499808236450613e+04
>>   F-Norm            =          nan
>> 
>> Fatal error: ci = -2147483648 should be in 0 .. 391 [FILE nsgrid.c, LINE 214]
>
>Is there something I am doing wrong?
To check quickly whether it is the charge you can ofcourse replace 12
solvents by Na+ (using genion).

>I realize that a net charge for periodic systems leads to infinite
>energies, but I assume this is all taken care of in the G=0 term of the
>FFT's. Is this correct?
I'm not sure to be honest. The 0,0,0 term is not taken into account in
computation of forces and charges.

Groeten, David.
________________________________________________________________________
Dr. David van der Spoel, 	Biomedical center, Dept. of Biochemistry
Husargatan 3, Box 576,  	75123 Uppsala, Sweden
phone:	46 18 471 4205		fax: 46 18 511 755
spoel at xray.bmc.uu.se	spoel at gromacs.org   http://zorn.bmc.uu.se/~spoel
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