OT vs. diagonalization

[mpol]

Dear CP2k developers and users,

Diagonalization instead of OT is suggested for KS wavefunction optimization 
in case of metals. But what about systems with small gap (semiconductors, 
transition metal clusters without ligands, etc.) or gapless systems (like 
e.g. graphene), can we use OT in these cases? Let's consider graphene, if 
one choses the supercell in a way that Dirac point is folded at 
gamma-point, the "gap" values may be small (~0.01 eV), even below the 
accuracy of currently available DFT methods. Can one use FULL_ALL 
preconditioner with ENERGY_GAP parameter equal to e.g. 0.0001 Ha in 
mentioned cases (small or zero gap)?

With best regards,
MP
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