  We go further on the study of harmonicity for almost contact metric
structures already initiated by Vergara-Diaz and Wood. By using the intrinsic
torsion, we characterise harmonic almost contact metric structures in several
equivalent ways and show conditions relating harmonicity and classes of almost
contact metric structures. Additionally, we study the harmonicity of such
structures as a map into the quotient bundle of the oriented orthonormal frames
by the action of the structural group U(n)x1. Finally, by using a Bochner type
formula proved by Bor and Hernandez Lamoneda, we display some examples which
give the absolute minimum for the energy.
