[Wien] GMAX = 15 causes xcpot3 error in LAPW0

[Thomas Claesson]

Thanks a lot for your very quick and detailed answer!

Best regards,
Thomas Claesson

Laurence Marks wrote:
> The size of the FFT parameters are set in case.in0 with default values
> when you initialize the calculation, in your case to 32 32 32. This is
> for the default GMAX=12 (unless you have H's in which case it is
> presumably GMAX=20). A simple fix is to edit the last line of case.in0
> to read
> 
>   -1 -1 -1    2.00    min IFFT-parameters, enhancement factor
> 
> The "-1" tells lapw0 to work out itself what to use depending upon the
> maximum k-value it finds and then use a times 2 enhancement (really an
> oversampling in reciprocal space).
> 
> Alternatively you can put 32*16/12 i.e. 43 (rounded up) instead of 32.
> 
> On 10/9/07, Thomas Claesson <tcl at kth.se> wrote:
>> Dear Wien users and developers!
>>
>> My question concerns the parameter GMAX. I have seen a comment on the
>> mailing list about the importance of not using a too small value of GMAX
>> in order to avoid discontinuities in the charge density at the sphere
>> boundary. With an RKmax value of 7.0 I increased GMAX to from 12 to 15,
>> which resulted in the following error in LAPW0:
>>
>>  'SETFF1' - ifft too small in xcpot3
>>  'SETFF1' - 2*(KKK+1) LARGER THAN IFFT PARAMETERS IN XCPOT3
>>  'SETFF1' - KKK=   0   0  16
>>  'SETFF1' - IIx=   0   0  16
>>  'SETFF1' - IFFT=  32  32  32
>>
>> So I would like to know, why can't I use use GMAX > 14 in my case? I have
>> tried to increase RKmax to 8.0 but that had no effect on the problem with
>> GMAX. Are the possible  values of RKmax and Gmax related to each other? If
>> so, how can I determine which RKmax value to use for a specific choice of
>> GMAX?
>>
>> Any comments are welcome! Thanks in advance for your replies.
>>
>> Best regards, Thomas Claesson
>>
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> 
>