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An idealized arrangement of confined DNA as approximately concentric loops around a central hole, with neighboring strands locally close-packed. It separates curvature-dependent DNA bending energy from interstrand interactions. It is a geometrical model, not a universal experimentally established arrangement in every capsid.

For an inextensible worm-like chain, the DNA bending energy iswhere $\kappa$ is curvature and $\ell$ is polymer contour length. A circle of radius $R_i$ has $\kappa =1/R_i$ and length $2\pi R_i$. Its elastic energy is therefore $(k_{B}T{l}_p/2)(2\pi R_i)/R_i^2=\pi l_p{k}_{B}T/R_i$. Adding the contributions of $n(R_i)$ rings at each radius givesThis ignores short connecting segments, twist, interactions between neighboring DNA segments and end effects. In a cylindrical stack with axial spacing $s$, $n(R_i)\simeq h/s$ away from the ends.

The specified screened-sphere charging model gives $8.00\times 10^5\mathrm{pN}\mathrm{nm}$, about $3.8$ times the supplied experimental magnitude. It is much closer than the unscreened result. The separate ideal counterion-compression estimate gives $1.91\times 10^5\mathrm{pN}\mathrm{nm}$, within about $9\%$ of that magnitude, but this numerical proximity does not validate its rough geometry.

Remaining differences can arise from the unpacked reference self-energy, counterion condensation, ion exchange with the surrounding reservoir, nonuniform charge density, nonlinear electrostatic screening, finite DNA thickness and the actual capsid shape. DNA bending energy, hydration forces and configurational entropy also contribute. The experiment measures a process-dependent work or inferred free energy, whereas the simple screened sphere computes just one model contribution. Neither a zero-net-charge argument nor agreement of one approximate number establishes an exact total energy.