Number of electrons can be large than number of orbitals (or equal)

[foxtran]

Describe the bug
For systems with an extra electrons, the condition that # electrons equals # orbitals that may lead to out-of-bounds access, for example, here:

xtb/src/scc_core.f90

Line 974 in c3cfd38

e_fermi = 0.5*(eig(nel)+eig(nel+1))

And therefore, there is a out-of-bounds memory access.

To Reproduce
Steps to reproduce the behaviour:

1. Use the latest version (from git repo)
2. Add manual check near src/scc_core.f90#L974
3. xtb h2.xyz --chrg 1
4. See your message :-)

Expected behaviour
Properly catching cases when number of electrons achieves number of orbitals.

Additional context
Add any other context about the problem here.

H2.xyz:

2

H 0.7 0.0 0.0
H 0.0 0.0 0.0

[marvinfriede]

Thanks for reporting. You also see the issue by just looking at the Fermi level.

xtb h2.xyz --ceasefiles --chrg 1 | grep "Fermi-level"

This shows:

Fermi-level NaN Eh NaN eV