  We use molecular dynamics simulations to unravel the physics underpinning the
light-induced density changes caused by the dynamic trans-cis-trans
isomerization cycles of azo-mesogens embedded in a liquid crystal polymer
network, an intriguing experimental observation reported in the literature. We
employ two approaches, cyclic and probabilistic switching of isomers, to
simulate dynamic isomerization. The cyclic switching of isomers confirms that
dynamic isomerization can lead to density changes at specific switch-time
intervals. The probabilistic switching approach further deciphers the physics
behind the non-monotonous relation between density reduction and light
intensities observed in experiments. Light intensity variations in experiments
are accounted for in simulations by varying the trans-to-cis and cis-to-trans
isomerization probabilities. The simulations show that an optimal combination
of these two probabilities results in a maximum density reduction,
corroborating the experimental observations. At such an optimal combination of
probabilities, the dynamic trans-cis-trans isomerization cycles occur at a
specific frequency, causing significant distortion in the polymer network,
resulting in a maximum density reduction.
