Parameter choice for GAPW

[Marcella Iannuzzi]

Hi Ali, 

As already said in the previous reply, by applying the GAPW scheme, the 
density is going to be partitioned in soft and hard terms also when PP are 
used. 
The large number of parameters that could be tuned might be of some help in 
difficult cases, but often the default values are a good first choice.

Which basis set functions are going to contribute to the local densities 
depends on the exponents of the primitives. Actually, the threshold is 
determined by the EPSFIT parameter. Anyway, I would use the default for 
that.

The compensation charges are described in terms of an expansion in Gaussian 
terms with the exponent alpha0_hard. Also in this case the default value 
should be ok. 
The 3 center terms are not computed anymore. From our tests it turns out 
that there is no loss in accuracy by imposing the soft and hard local 
compensation charges to be the same. This cancels the 3c terms. Hence the 
eps_3c_reduce is not used anymore. It is a left over and I am going to 
remove it from the code. 

>From the input reference manual should be clear which eps_*** are affected 
by eps_default. These are all parameters used by both gpw and gapw in the 
same way.

The  lmaxn1 is determined automatically from the GTO basis sets that you 
have chosen. This is the meaning of -1
Setting this from input to a smaller value would reduce the accuracy and 
maybe improve in performance. 
I wouldn't do it, if not necessary. 

The quadrature schemes are equivalent. 

The number of points for the local grids can affect the accuracy. But 
normally reasonable grids are already obtained with lebedev between 50 ad 
80 and radial between 100 and 200. Depends on the element and basis sets 
anyway. 

You can always check whether the results are converged with respect to 
these parameters, by modifying them. This should give you a feeling on how 
sensitive the calculation is to them.

Kind regards

Marcella


On Saturday, June 21, 2014 1:23:47 PM UTC+2, Ali Akbari wrote:
>
> Hi,
>
> I appreciate if someone tells me is it possible to use pseudo potential 
> with GAPW
> treatment? I was reading the following discussion to find the necessary 
> parameters: 
> https://groups.google.com/forum/#!msg/cp2k/RUFQScjSDn0/At_pJzz49_oJ
>
> What changes if I have a mixture of pseudo potential for some atoms and all
> electron for others? e.g. Do I still need to choose the  HARD_EXP_RADIUS
> such that there is no overlap between a pseudo atom and all electron atom?
>
> Many thanks and cheers,
> Ali
>
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