[CP2K:1389] Re: EMAX_SPLINE too small

Laino Teodoro teodor... at gmail.com
Thu Oct 2 11:24:33 UTC 2008


> So I set the charges exactly as shown if the distribution test files,

This is the premise:
distribution tests are there to test some functionalities.. never  
trust them for
whatever production run. If you want to use something within CP2K get  
to make your hands dirty with the code.. otherwise you'd better use  
some more
well documented program (until there will be some clear documentation  
of course)...

In detail:
What I said in the previous e-mail is partially wrong. Let me correct:
If your atom type has a core-shell specification the value of the  
charge in FORCEFIELD%CHARGE is just ignored.
For your input file, this is not the case for Si, while it is for O.
So.. the information FORCEFIELD%CHARGE for the O is ignored but not  
for Si.
For the calculation itself does not make any difference if you use  
but for cleanness I would avoid to have it in the input file.. (will  
put a warning when that value is ignored).

> ------------> CHARGE_INFO| Total Charge of the Classical
> System:                     0.000000
> I've tried to set the charge of O to zero and kept the charge coming
> from the shell-core part but cp2k displays a positive total charge for
> the system.
> so, I do not see what do you mean by setting charge of O to zero and
> keep the charge flowing from the shell-core part !!!!!!

This is an I/O bug and I will fix ASAP. The charge value displayed  
does not account for the
CORE-SHELL contribution and it's clearly a bug. This bug does not  
affect the calculation.

> second point is the EMAX_SPLINE itself. I've tried to increase it but
> the simulation start running only with a value higher than 300
> hartree !!! does this really need to be that high ????

well.. this means that:
(1) cell and geometry do not match
(2) the way you inputed the potential is wrong (maybe units). Check it!
(3) geometry is wrong.

> fourth point, a timestep of 0.2 fs should be enough to capture the
> movements of the shell-core couples especially with a high force
> constant (using DLPOLY for example, simulations with a shell model and
> with 0.2 fs is stable without drift of energy).

I already said that 0.2 is a good starting point. I just told you to  
check carefully that your dynamics is
a conserved one. Exporting this expertise from other programs is IMHO  
quite dangerous.. implementations
are different.. so as I said check if you want to be sure to do  
something meaningful.

> last point, I changed everything as you advised but the system
> collapsed.

Putting the charge of O to zero cannot be the reason for the  
collapsing, since that value
as I already said is IGNORED. If your system collapse and the geometry 
+cell are ok, then
check the definition of your potential (which maybe the reason why  
you need such a huge emax_spline
and nonetheless the system collapse).


> So, can you please do me a favor and check this again
> closely ??????????????????

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