VBS State Induced by Impurity Frustration in Cr8Ni

We provide a physically meaningful picture of the nature of the ground state of the Cr8Ni compound in the regime where it is a spin singlet. According to this picture, the anisotropy of the $Ni$ atom in the $Cr$ ring induces a dimerization in the molecule that makes the ground state to stabilize in a Valence Bond Solid phase of virtual spins. We characterize rigorously this phase by means of a particular non-local order parameter denoted the generalized string order parameter. In the completely antiferromagnetic regime, the system becomes frustrated. We have performed a numerical real-time evolution study of the correlations between the spin of the $Ni$ impurity and the rest of the spins in order to show the reaction of the system under this frustration. We provide results that manifestly show the agreement with the Valence Bond Solid picture introduced.