  The non-additive dispersion contribution to the binding energy of three
one-dimensional (1D) wires is investigated using wires modelled by (i) chains
of hydrogen atoms and (ii) homogeneous electron gases. We demonstrate that the
non-additive dispersion contribution to the binding energy is significantly
enhanced compared with that expected from Axilrod-Teller-Muto-type
triple-dipole summations and follows a different power-law decay with
separation. The triwire non-additive dispersion for 1D electron gases scales
according to the power law $d^{-\beta}$, where $d$ is the wire separation, with
exponents $\beta(r_s)$ smaller than 3 and slightly increasing with $r_s$ from
2.4 at $r_s = 1$ to 2.9 at $r_s=10$, where $r_s$ is the density parameter of
the 1D electron gas. This is in good agreement with the exponent $\beta=3$
suggested by the leading-order charge-flow contribution to the triwire
non-additivity, and is a significantly slower decay than the $\sim d^{-7}$
behaviour that would be expected from triple-dipole summations.
