Quickstep: SCF Energy increasing after few outer-SCF cycles

[Florian Schiffmann]

Hi, 

this problem has indeed to do with the preconditioner. The statement on the 
website that a 0.001 value for the energy gap should improve convergence is 
only partially true. The problem is that it is used as a scaling factor, 
which for well behaved system (wide band gap usually) is not a problem, but 
can lead to more random results (problems in inversion due to almost linear 
dependencies) for small band gap systems and thus mess up your electronic 
structure (see electronic density on regular grids). Changing the value for 
the energy gap to 0.1 should thus help as well. As always check as well 
your plane wave convergence, especially for BLYP larger values might be 
required.

Flo
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