AMBER Archive (2004)

Subject: Re: AMBER: Ewald parameter range

From: Johnson Agbo (agboj_at_chem.unr.edu)
Date: Fri Jul 23 2004 - 13:00:12 CDT


Hi David;
Thanks for the information, changing the skinnb value to 1 works. Much
appreciation.

On Jul 23, 2004, at 1:53 AM, David A. Case wrote:

> On Thu, Jul 22, 2004, Johnson Agbo wrote:
>
>> I am running minimization and dynamics on cubic ice with periodic
>> boundary conditions,
>
> Amber has limitations in simulating small unit cells. Basically, the
> cutoff + "skin" has to be less than half of the unit cell size.
>
>>
>> Ewald PARAMETER RANGE CHECKING:
>> parameter skinnb+cutoffnb: (nonbond list cut) has value 0.10000E+02
>> This is outside the legal range
>> Lower limit: 0.00000E+00 Upper limit: 0.95370E+01
>
> So, you need to use a smaller cutoff + skin (probably by reducing
> skinnb
> from its default value of 2 to a value of 1), or create a bigger unit
> cell.
>
>> I went into the program file ( ew_legal.h ) and changed the
>> coefficients to the values shown below,
>> ( _REAL_ ew_coefflo,ew_coeffhi
>> parameter(ew_coefflo=0.0d0,ew_coeffhi=17.d0)
>
> Your problem has really nothing to do with the ewald coefficeint....
>
> ...dac
>
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