diff --git a/.gitignore b/.gitignore
index a00f4f4..9996755 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
 *.build_distribution
+.gitignore
diff --git a/TenNet/__pycache__/__init__.cpython-38.pyc b/TenNet/__pycache__/__init__.cpython-38.pyc
index e988dc7..5b160a3 100644
Binary files a/TenNet/__pycache__/__init__.cpython-38.pyc and b/TenNet/__pycache__/__init__.cpython-38.pyc differ
diff --git a/TenNet/spin_systems/Hamiltonians.py b/TenNet/spin_systems/Hamiltonians.py
index aeebed2..2b83aed 100644
--- a/TenNet/spin_systems/Hamiltonians.py
+++ b/TenNet/spin_systems/Hamiltonians.py
@@ -40,9 +40,9 @@ def IsingChainWithAncilla(L, J=1., h_z=1., h_x=0.):
     Wbulk[0,0,:,:] = np.eye(4)
     Wbulk[1,0,:,:] = Xsys
     Wbulk[2,0,:,:] = Xanc
-    Wbulk[3,0,:,:] = -h_x*(Xsys+Xanc)-h_z*(Zsys+Zanc)
+    Wbulk[3,0,:,:] = -h_x*(Xsys-Xanc)-h_z*(Zsys-Zanc)
     Wbulk[3,1,:,:] = -J*Xsys
-    Wbulk[3,2,:,:] = -J*Xanc
+    Wbulk[3,2,:,:] = J*Xanc
     Wbulk[3,3,:,:] = np.eye(4)
     
     tensors[0]  = (Wbulk[-1,:,:,:].copy()).reshape(1,4,4,4)