Minimal energy packings of nearly flexible polymers

TL;DR

This paper investigates how adding bond-angle interactions affects the minimal energy packings of short flexible polymers, revealing a critical stiffness ratio where the energy landscape and conformations change significantly.

Contribution

It extends previous models by incorporating bond-angle interactions and identifies the critical stiffness ratio where polymer packing behavior shifts.

Findings

Flexible tangent sticky-hard-sphere packings serve as a basis for analysis.

A critical ratio of bending to pair stiffness determines the structural transition.

Increasing bending stiffness dramatically alters the energy landscape and conformations.

Abstract

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.