Influence of shear strain on stability of 2D triangular lattice

Stability of 2D triangular lattice under finite arbitrary strain is investigated. The lattice is considered infinite and consisting of particles which interact by pair force central potential. Dynamic stability criterion is used: frequency of elastic waves is required to be real for any real wave vector. Two stability regions corresponding to horizontal and vertical orientations of the lattice are obtained. It means that a structural transition, which is equal to the change of lattice orientation, is possible.