The maximum surface area polyhedron with five vertices inscribed in the sphere {\bb S}^{2}

Acta Crystallogr A Found Adv. 2021 Jan 1;77(Pt 1):67-74. doi: 10.1107/S2053273320015089. Epub 2021 Jan 5.

Abstract

This article focuses on the problem of analytically determining the optimal placement of five points on the unit sphere {\bb S}^{2} so that the surface area of the convex hull of the points is maximized. It is shown that the optimal polyhedron has a trigonal bipyramidal structure with two vertices placed at the north and south poles and the other three vertices forming an equilateral triangle inscribed in the equator. This result confirms a conjecture of Akkiraju, who conducted a numerical search for the maximizer. As an application to crystallography, the surface area discrepancy is considered as a measure of distortion between an observed coordination polyhedron and an ideal one. The main result yields a formula for the surface area discrepancy of any coordination polyhedron with five vertices.

Keywords: inequalities; optimization; polyhedra; surface area; triangular bipyramids.