Frustration freeness
= Frustration freeness
{title2=$E_0(H)=\sum_ZE_0(h_Z)$}
A decomposition $H=\sum_Zh_Z$ has <frustration freeness> when a global <ground state> minimizes every term simultaneously. For finite-dimensional Hermitian terms this implies $E_0(H)=\sum_ZE_0(h_Z)$. Shifting each term by its minimum produces <positive operators> with a common null vector. The property depends on the decomposition, not only the total operator.