= Solution
The specified screened-sphere charging model gives $8.00\times10^5\,\mathrm{pN\,nm}$, about $3.8$ times the supplied experimental magnitude. It is much closer than the unscreened result. The separate ideal <counterion>-compression estimate gives $1.91\times10^5\,\mathrm{pN\,nm}$, 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.
Back to article page
