Distorted AB-pair graphene cluster model
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Interpretation used for this project:
- 6-site supercell with labels A, A', B, B', C, C'
- coordinates are explicitly distorted in real space
- each original A-B pair is pulled together inside the enlarged cell
- onsite energies are all equal to zero
- nearest-neighbor hopping only
- hopping is generated from the distorted bond length through
  t(d) = t0 * exp[-beta * (d/a0 - 1)]

pair_shift = 0.120000
t0 = 1.000000
beta = 3.370000

Supercell vectors:
T1 = (2.598076, 1.500000)
T2 = (-2.598076, 1.500000)

6x6 Bloch Hamiltonian:
H_ij(k) = sum_R t_ij(R) exp[i k dot (R + r_j - r_i)]

Unique nearest-neighbor distances / hoppings:
d = 0.760000, t(d) = 2.245212
d = 1.139122, t(d) = 0.625726

Direct gap from reciprocal-space grid = 1.987520