The XY Hamiltonian still has the Ising van der Waals interaction terms, so we should include them in the Hamiltonian.
The terms are given by
$$ \frac{C_6}{R_{ij}^6} (1-\hat{n}_i) (1-\hat{n}_j),~~~~n = |0\rangle\langle 0|$$
@LucasGitQ can you please confirm if this is correct (particularly the definition of $n$)?
The XY Hamiltonian still has the Ising van der Waals interaction terms, so we should include them in the Hamiltonian.
The terms are given by
@LucasGitQ can you please confirm if this is correct (particularly the definition of$n$ )?