Discrete gap breathers in chains with strong hydrogen bonding

We consider a diatomic chain of heavy ions coupled by hydrogen bonds which are sufficiently strong compared with other interactions in the system. In this case, each proton in the hydrogen bond is subject to a single-minimum potential resulting from its interaction with nearest-neighbor heavy ions through the Morse potential that contains soft anharmonicity. This diatomic chain of nonlinearly coupled masses admits discrete breather solutions in the gap of the phonon spectrum. Simple analytical arguments accompanying explicit solutions that demonstrate the existence of the gap breather with only one type of symmetry, namely the odd-parity pattern centered at a hydrogen-bonded proton, are present. These arguments are supported by the numerically exact procedure using the anticontinuous limit. Some other multi-breather solutions in the gap are also obtained exactly from the anticontinuous limit.