[Wannier] explicit supercell calculation

[Aaron M]

For the testing purposes of another program that uses the output of
wannier90 I'm trying to run a Gamma centered Monkhorst-Pack k-sampled
calculation and then run the equivalent Gamma sampled supercell
calculation. My first test system was a loosely bound H2 chain, which
behaved as expected. The scf/nscf/wannier90 (using QEv6.5) all matched
exactly for the k-sampled and explicit supercell calculations in Bloch
orbital energy spectrum and Wannier function spreads and centers. Then I
attempted to do the same for silicon, and have been unable to get the same
results. The scf/nscf Bloch orbital energy spectrums agree as expected, but
the supercell calculation does not localize correctly. During the descent
phase the SPRD jumps around wildly and does not nicely descend like it does
in the k-sampled case. The initial guesses I have tried are
use_bloch_phases=.true., and SCDM isolated since I'm only using the
occupied orbitals. I have also tried using the gamma branch algorithms for
the supercell and surprisingly saw that the SPRD does not always decrease,
which makes no sense to me from my understanding of how the 2x2 rotation
algorithm works. I don't know if I'm doing something wrong or if this is
expected behavior? Any help would be appreciated. Attached are the input
files I used for the silicon calculation with an mp_grid = 4 4 4 and the
equivalent unfolded supercell. Cheers,
-Aaron Mahler
Duke University

PS: I'm using these pseudos: https://github.com/pipidog/ONCVPSP
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