  We conduct a theoretical investigation on the existence of Barren Plateaus
for alternated disentangled UCC (dUCC) ansatz, a relaxed version of Trotterized
UCC ansatz. In the infinite depth limit, we prove that if only single
excitations are involved, the energy landscape of any electronic structure
Hamiltonian concentrates polynomially. In contrast, if there are additionally
double excitations, the energy landscape concentrates exponentially, which
indicates the presence of BP. Furthermore, we perform numerical simulations to
study the finite depth scenario. Based on the numerical results, we conjecture
that the widely used first-order Trotterized UCCSD and $k$-UpCCGSD when $k$ is
a constant suffer from BP. Contrary to previous perspectives, our results
suggest that chemically inspired ansatz can also be susceptible to BP.
Furthermore, our findings indicate that while the inclusion of double
excitations in the ansatz is essential for improving accuracy, it may
concurrently exacerbate the training difficulty.
