Lower energy with larger basis set


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Hello,

I am running all-electron DFT calculations for single atoms and I am interested in the total energy. As DFT is variational one expects the larger basis sets to yield lower total energies, which is also the case in most of my calculations, except for the aug-cc-pv6z basis which yields a higher total energy ( -128.226194282698 a.u.) than the aug-cc-pv5z basis (-128.227026486337 a.u.). Can there be an error in the implementation of the basis, are some parameters like the grid for the integration not choseb appropriately or can this really happen from the way the aug-cc-pc6z basis is set up ?

The input file I use is

title "Ne"
echo
geometry units angstroms
Ne      0.0  0.0  0.0
end
basis
Ne library aug-cc-pv6Z 
end
dft
grid xfine
xc slater perdew81 
end
TASK DFT


Thanks for your answers

Volker