# Unphysical results with custom Mg basis set

Richard Fogarty richard.... at gmail.com
Tue Sep 11 12:31:31 CEST 2018

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.

Richard

Misc info:
This is using cp2k-6.1 in serial mode (cp2k.sopt executable)
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