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Minimal energy packings of nearly flexible polymers

We extend recent studies of the minimal energy packings of short flexible polymers with hard-core-like repulsions and short-range attractions to include bond-angle interactions with the aim of describing the collapsed conformations of `colloidal' polymers. We find that flexible tangent sticky-hard-sphere (t-SHS) packings provide a useful perturbative basis for analyzing polymer packings with nonzero bending stiffness only for {\it small} ratios of the stiffnesses for the bond-angle ($k_b$) and pair ($k_c$) interactions, i.e. $k_b^{\rm crit}/k_c \lesssim 0.01$ for $N<10$ monomers, and the critical ratio decreases with $N$. Below $k_b^{crit}$, angular interactions give rise to an exponential (in $N$) increase in the number of distinct angular energies arising from the diversity of covalent backbone paths through t-SHS packings. As $k_b$ increases above $k_b^{crit}$, the low-lying energy landscape changes dramatically as finite bending stiffness alters the structure of the polymer packings. This study lays the groundwork for exact-enumeration studies of the collapsed states of t-SHS-like models with larger bending stiffness.