The J1–J2 model is a quantum spin model like the Heisenberg model but also includes a term for the interaction between next-nearest neighbor spins.

In this model, the term ${\displaystyle J_{1))$ represents the usual nearest-neighbor interaction as seen in the Heisenberg model, and ${\displaystyle J_{2))$ represents the exchange interaction to the next nearest-neighbor.

${\displaystyle {\hat {H))=J_{1}\sum _{\langle ij\rangle }{\vec {S))_{i}\cdot {\vec {S))_{j}+J_{2}\sum _{\langle \langle ij\rangle \rangle }{\vec {S))_{i}\cdot {\vec {S))_{j))$

• Spin model
• Heisenberg model (quantum)
• Hubbard model
• t-J model
• Majumdar–Ghosh model

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