We investigate when the energy that pins a superfluid vortex to the lattice of nuclei in the inner crust of neutron stars can be approximated by the energy that binds the vortex to a single nucleus .
Indeed , although the pinning energy is the quantity relevant to the theory of pulsar glitches , so far full quantum calculations have been possible only for the binding energy .
Physically , the presence of nearby nuclei can be neglected if the lattice is dilute , namely with nuclei sufficiently distant from each other .
We find that the dilute limit is reached only for quite large Wigner-Seitz cells , with radii R _ { { } _ { WS } } \gtrsim 55 fm ; these are found only in the outermost low-density regions of the inner crust .
We conclude that present quantum calculations do not correspond to the pinning energies in almost the entire inner crust and thus their results are not predictive for the theory of glitches .