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Stability of optically bound cluster, in the Lyapunov sense, is governed by the force constant matrix (or stiffness matrix), which is the first order Taylor Series Expansion about equilibrium, and it determined the stability and vibration frequencies.
The openness of light matter interaction, i.e. the incident wave propagates, the scattered wave propagates outward, and absorption, caused non-conservative forces, making the force constant matrix non-symmetric (non-Hermitian). This opens up the possibility of having unstable vibrational modes with complex frequencies when the system is driven beyond its exceptional point, i.e., the non-conservative force is strong compare to the “gap” between adjacent vibrational frequencies.
Noting that in large scale optical binding, the “gap” goes to zero. The Lorentz force alone will not be sufficient in general to ensure the stability of optically bound structure. Other forces, such as hydrodynamic damping in water, is essential.
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