Used by the Chebyshev filter only.
Octopus generates a best-estimate for the degree of the Chebyshev polynomial used to filter the subspace.
A separate estimate is generated for each state block, per SCF iteration. Note that if running parallelism
over states, the block/batch containing the largest eigenstates will converge more slowly and will
therefore use a larger degree relative to all other batches. One should therefore avoid setting "ChebyshevFilterDegree"
to an excessive value (for example > 50). For more details regarding how the degree is estimated, one can refer to Section 5.4
in "Computer Physics Communications 187 (2015) 98–105" (http://dx.doi.org/10.1016/j.cpc.2014.10.015).