[ase-users] [ase-developers] ASE calculator interface proposal

[Jussi Enkovaara]

On 2013-01-23 17:43, Jens Jørgen Mortensen wrote:
> Den 23-01-2013 15:51, John Kitchin skrev:
>> Here are a few of my thoughts. They are based on my experiences with
>> Jacapo and jasp, and how I like/want to run my calculations. Some of
>> them may be somewhat controversial ;)
>
> Thanks for your comments and ideas.  I don't think they are that
> controversial.  My comments are below.

Hi,
I give below also some comments.

>> 2. Should there be a way to get a reasonable number of k-points for
>>    the given cell?
>>
>> It is hard to see how this is possible. How would the way know if you
>> had a slab, or atom, non-periodic boundary conditions in some
>> dimension? The requirements for metals are very different than
>> insulators.
>
> I agree.  This is too difficult.

I think the k-points density parameter is closest one can do here.
That should take care of the different boundary conditions and cell
sizes, however, the different requirements for metals, magnetic systems
etc. are something that the user has to know.

>> * Restart
>> There is another use mode worth discussing. In the following example:
>>
>> myatoms = Atoms(..., ideal positions)
>>
>> calc = MyCalculator(arg1, atoms=myatoms, kwargs)
>> # I greatly prefer this to myatoms.set_calculator(calc)
>> atoms.get_potential_energy()
>
> I like that way of attaching the calculator to the atoms.  I'll put that
> idea in the proposal.
 >
 >> 1. The first time you run this, a calculation get run.

As a personal preference :-), I do not like that heavy calculations get 
run when one creates an object (even though some GPAW functionality 
behaves this way), but that user has to explicitly request calculation 
by calling a function.

Also, I think that the above approach brings up the question whether 
one attaches atoms to a calculator, and asks calculator to determine 
physical quantities for this atomic configuration, or attaches 
calculator to atoms and asks physical quantities from atoms object, i.e. 
which comes first, atoms or calculator? There is already some 
controversy as some quantities are requested from atoms (energy, 
forces), and some from the calculator (wavefunctions, densities). 
Personally, I do not have strong feelings over this matter, asking atoms 
is maybe a little bit more physics oriented (calculator is just black 
box providing numbers), on the other hand asking calculator would unify 
things in the sense that everything is requested from calculator 
(quantities available from MD calculator are of course quite different 
than the ones availabe from DFT calculator).

One question that should maybe also discussed is if there should 
standard way to specify the command/binary to be executed when 
calculator is run. Some calculators (e.g. Siesta) request a python 
script containing the actual command to be executed, while other 
calculators (e.g. Castep) ask for a shell command. I prefer the shell 
command, as it is easier to specify e.g. number of CPUs within a batch 
job script (at least for casual user who is used to do something like 
'mpirun -np 8 siesta'). People wanting to script everything may prefer 
the first option...

Best regards,
Jussi