Degenerate Ground state about hphi HOT 1 CLOSED

@rp092
In quantum systems, you can obtain the superposition
of the doubly degenerate classical charge ordered states
(In this superposition, translational symmetry is not broke).

Actually you can confirm this by performing the
full diagonalization using HPhi (sample input file is shown below).

model = "Hubbard"
method = "fulldiag"
lattice = "chain"
L = 6
V = 4.0
t = 1.0
2Sz = 3
nelec = 3

For L=8 or more generally even sites,
you can obtain doubly degenerate
ground states due to the accidental degeneracy
in the total momentum (K=0,pi).
In the double degenerate states obtained by HPhi,
the translational symmetry is apparently broken
because the states with different total momentum mix each other.

You can obtain the charge uniform state
by properly specifying the total momentum.
Unfortunately, we do not implement such function in HPhi.
Thus, if you want to specify the total momentum,
it is necessary to change the codes properly.

from hphi.