Make threshold in energy change during CG iterations a parameter (CGEnergyChangeThreshold)

Description

CG iterations for each band are stopped when the change in energy falls below the first change in energy time this factor, which defaults to 0.1. For LDA and GGA functionals, this reduces the total runtime by doing less CG iterations per SCF cycle. For OEP this should probably lower, 1e-3 or less. In general, if there convergence problems, one can try decreasing this value.

News snippet

Make threshold in energy change during CG iterations a parameter.

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