  Thermal entanglement of a geometrically frustrated spin-1 Heisenberg diamond
cluster is examined within the framework of the exact diagonalization method by
computing the measure of entanglement negativity. The calculated exact
analytical results are applied in order to obtain theoretical prediction of the
robustness of bipartite thermal entanglement of the tetranuclear nickel complex
[Ni4(CO3)2(aetpy)8](ClO4)4 (aetpy = 2-aminoethyl-pyridine) against rising
temperature and magnetic field.
