# Unphysical results with custom Mg basis set

Richard Fogarty richard.... at gmail.com
Tue Sep 11 17:35:01 CEST 2018

Hi Matthias,

Thank you for the response. I had overlooked the basis sets in the
BASIS_MOLOPT_UCL file. Unfortunately these basis sets are unlikely to be
suitable for my purpose which (as i should have mentioned in my original
post) is to use the basis set to build a tight binding model (which has
different requirements to KS-DFT basis sets, e.g. shorter ranged orbitals
are preferred). The reason I'm doing cp2k calculations is essentially to
estimate the errors that arise from using this basis set (compared to a
more complete one).

I will look into using the GTH-q10 PP if i cant get the accuracy i need
with the q2 basis-set, so thanks for the suggestion.

Thanks
Richard

On Tuesday, September 11, 2018 at 11:31:31 AM UTC+1, Richard Fogarty wrote:
>
> Dear all,
>
> I'm trying to use a custom basis-set for Mg in CP2K but am getting
> unphysical results; I suspect the reason is that i'm making a mistake with
> the basis set formatting. The simplest unphysical result is for a
> calculation on a single atom, whereby the ground state has p-orbitals
> (rather than s) fully occupied (see attached *.inp and *.cpout files).
>
> The basis set is generated in an external program using the following
> steps:
> 1) A calculation is carried out on an Mg atom with the s-shell occupied
> (neutral atom, no net spin). This calculation yields a list of grid points
> (distances from the nucleus, due to the spherical symmetry), and the value
> of each shell at these grid points (which I'll call *\phi_{r}*). I'm
> using the same pseudopotential ("Mg GTH-PBE-q2") in this calculation as in
> the subsequent CP2K calculations.
> 2) The value of *\phi_{r}* is multiplied by sqrt((2l+1))*(r**l)
> 3) Gaussians are fit to the data from step 2.
>
> Im loading the exponents and coefficients from step 3) into CP2K. One
> example is attached (file MG_TEST_BASIS). Note that the basis set attached
> leads to reasonable results for a single atom in the external program
> (where i know im entering it in the correct format).
>
> Any help would be greatly appreciated.
>