We prove that for α ≥ 1, among 2d unit density lattices, minLPL(|P|2β)eπα|P|2 is achieved at hexagonal lattice for β12πα and does not exist for β>12πα. Here the hexagonal lattice with unit density can be expressed by Λ1=132[Z(1,0)Z(12,32)]. This leads to two applications as follows. (1) Assume that α ≥ 1. Then, among 2d unit density lattices, minLPL|P|2eπα|P|2 is achieved at hexagonal lattice. (2) Assume that β > α ≥ 1. Then minzHθ(α;z)bθ(β;z) is achieved at z=eiπ3 (corresponding to hexagonal lattice) for bβα and does not exist for b>βα. Here θ(αz) is the two-dimensional Theta function.

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