Peierls-Nabarro potential barrier for highly localized nonlinear modes.

We consider two types of strongly localized modes in discrete nonlinear lattices. Taking the lattice nonlinear Schrodinger (NLS) equation as a particular but rather fundamental example, we show that (1) the discreteness effects may be understood in the "standard" discrete NLS model as arising from an effective periodic potential similar to the Peierls-Nabarro (PN) barrier potential for kinks in the Frenkel-Kontorova model; (2) this PN potential vanishes in the completely integrable Ablowitz-Ladik variant of the NLS equation; and hence (3) the PN potential arises from the nonintegrability of the discrete physical models and determines the stability properties of the stationary localized modes.