Starting from the single molecule energy and applying the methods

of statistical mechanics, the free energy of a lipid monolayer

(bilayer) is derived in this section (Fournier, 1996; Kralj-Iglicˇ,

2002; Kralj-Iglicˇ et al., 1999, 2006). The local bending energy of

a laterally homogeneous monolayer (bilayer) (see Canham, 1970;

Helfrich, 1973; Landau and Lifshitz, 1997; Petrov and Derzhanski,

1976) is obtained, and an additional contribution due to average

orientational ordering of lipid molecules-that is, the contribution

of the deviatoric bending (Fischer, 1992, 1993)—is derived (Kralj-

Iglicˇ, 2002; Kralj-Iglicˇ et al., 1999, 2006). The average orientational

ordering of anisotropic phospholipids lowers the free energy of the

system; the effect is more pronounced for lipid molecules of larger

anisotropy and stronger membrane curvature anisotropy (see Kralj-

Iglicˇ et al., 2006).