Used by the cg solver only. For each band, the CG iterations are stopped when the change in energy is smaller than the change in the first iteration multiplied by this factor. This limits the number of CG iterations for each band, while still showing good convergence for the SCF cycle. The criterion is discussed in Sec. V.B.6 of Payne et al. (1992), Rev. Mod. Phys. 64, 4. The default value is 0.1, which is usually a good choice for LDA and GGA potentials. If you are solving the OEP equation, you might want to set this value to 1e-3 or smaller. In general, smaller values might help if you experience convergence problems. For very small convergence tolerances, choose 0 to disable this criterion.
call parse_variable(namespace, 'CGEnergyChangeThreshold', CNST(0.1), eigens%energy_change_threshold)