\pi^2 \rho/ ({2{c_\mathrm{T}}^{-3} + {c_\mathrm{L}}^{-3}})
\right]^{1/3}$, and $c_\mathrm{L} =\sqrt{(K+4G/3)/\rho}$ and $c_\mathrm{T} = \sqrt{G/\rho}$ are the longitudinal and transverse sound speeds, respectively. Figure \[fig5\] presents the values of $\omega_\mathrm{D}$ and $A_\mathrm{D}$ as functions of $\varepsilon_\mathrm{bend}$. As the bulk modulus is approximately four times larger than the shear modulus, $\omega_\mathrm{D}$ and $A_\mathrm{D}$ are mostly determined with the shear modulus, i.e, $\omega_\mathrm{D} \approx \left( 9 \pi^2 \rho
\right)^{1/3} c_\mathrm{T}$ and $A_\mathrm{D} \approx 1/ \left(3 \pi^2 \rho
c_\mathrm{T}^3 \right)$.

As shown in Fig. \[fig4\], the polymer glasses present clear excess peaks over the Debye level, i.e., the BP. The BP frequency, $\omega_\mathrm{BP}$, is defined as the frequency at which $g(\omega)/\omega^2$ is maximal. As $\varepsilon_\mathrm{bend}$ increases, $\omega_\mathrm{BP}$ shifts to a higher frequency. In addition, the height of the reduced vDOS, $g(\omega_\mathrm{BP})/\omega_\mathrm{BP}^2$, becomes lower. These shifts are observed in the region from $\varepsilon_\mathrm{bend}=10$ to $10^3$ for $L=50$ and $3$. Importantly, this region corresponds to the shear modulus $G$ variations, as shown in Figs. \[fig3\]c and \[fig3\]d. As the bulk modulus is much larger than the shear modulus, the bulk modulus should only have minor effects on the low-frequency spectra. Therefore, the BP of the proposed system should only be controlled by the shear elasticity.

To confirm 