A potential that overcomes the objectionos with the cellular method is the Muffiin-tin potential, whcih is taken to represent an isolated ion within an spehere of radius around each lattice point, and taken to be constant elsewhere. The muffin-tin potential mitigates both problems, being flat in the intestitial region, and leading to matching conditions on a spherical, rather than a polyhedral surface.
Formally, the muffin-tin potential can be defined by:
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