J1-J2 Heisenberg Chain

Purpose and structure

This frustrated spin chain combines nearest- and next-nearest-neighbor Heisenberg exchange:

$$ H=J_1\sum_i\mathbf P_i\cdot\mathbf P_{i+1} +J_2\sum_i\mathbf P_i\cdot\mathbf P_{i+2}+g\sum_iZ_i, $$

with $\mathbf P=(X,Y,Z)$. Competition between $J_1$ and $J_2$ creates a compact frustration benchmark.

Basis and use

from quantum_lattice_models import j1_j2_heisenberg_chain

H = j1_j2_heisenberg_chain(n_sites=6, j1=1.0, j2=0.4)

The dense computational-basis dimension is $2^N$.

Parameters

User notes

Periodic next-nearest-neighbor bonds are defined only when enough distinct sites exist. The package uses Pauli products directly.