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Add chemical potential parameter mu to Hubbard model #199

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Merged
hzhangxyz merged 2 commits into from
Mar 5, 2026
Merged

Add chemical potential parameter mu to Hubbard model #199

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Copilot Mar 5, 2026
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Add chemical potential parameter mu to Hubbard model
Copilot Mar 5, 2026
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22 changes: 15 additions & 7 deletions qmp/models/hubbard.py
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Original file line number Diff line number Diff line change
Expand Up @@ -28,8 +28,11 @@ class ModelConfig:
t: float = 1
# The coefficient of U
u: float = 0
# The chemical potential mu
mu: float = 0

# The electron number, left empty for half-filling
# The electron number, left empty for half-filling.
# Note: if a network without particle number conservation is used, this parameter will be ignored.
electron_number: int | None = None

# The ref energy of the model
Expand Down Expand Up @@ -65,11 +68,6 @@ def _index(i: int, j: int, o: int) -> int:
hamiltonian_dict: dict[tuple[tuple[int, int], ...], complex] = {}
for i in range(args.m):
for j in range(args.n):
# On-site interaction
hamiltonian_dict[
(_index(i, j, 0), 1), (_index(i, j, 0), 0), (_index(i, j, 1), 1), (_index(i, j, 1), 0)
] = args.u

# Nearest neighbor hopping
if i != 0:
hamiltonian_dict[(_index(i, j, 0), 1), (_index(i - 1, j, 0), 0)] = -args.t
Expand All @@ -82,6 +80,15 @@ def _index(i: int, j: int, o: int) -> int:
hamiltonian_dict[(_index(i, j, 1), 1), (_index(i, j - 1, 1), 0)] = -args.t
hamiltonian_dict[(_index(i, j - 1, 1), 1), (_index(i, j, 1), 0)] = -args.t

# On-site interaction
hamiltonian_dict[
(_index(i, j, 0), 1), (_index(i, j, 0), 0), (_index(i, j, 1), 1), (_index(i, j, 1), 0)
] = args.u

# Chemical potential
hamiltonian_dict[(_index(i, j, 0), 1), (_index(i, j, 0), 0)] = -args.mu
hamiltonian_dict[(_index(i, j, 1), 1), (_index(i, j, 1), 0)] = -args.mu

return hamiltonian_dict

def __init__(self, args: ModelConfig):
Expand All @@ -90,11 +97,12 @@ def __init__(self, args: ModelConfig):
self.n: int = args.n
self.electron_number: int = args.electron_number
logging.info(
"Constructing Hubbard model: width = %d, height = %d, t = %.4f, U = %.4f, N = %d, ref_energy = %.4f",
"Constructing Hubbard model: width = %d, height = %d, t = %.4f, U = %.4f, mu = %.4f, N = %d, ref_energy = %.4f",
self.m,
self.n,
args.t,
args.u,
args.mu,
args.electron_number,
args.ref_energy,
)
Expand Down