  We show that in anharmonic one-dimensional crystal lattices pairing of
electrons or holes in a localized bisolectron state is possible due to coupling
between the charges and the lattice deformation that can overcompensate the
Coulomb repulsion. Such localized soliton-like states appear as traveling
ground bound singlet states of two extra electrons in the potential well
created by the local lattice deformation. We also find the first excited
localized state of two electrons in a soliton-like lattice deformation
potential well given by a triplet state of two electrons. The results of the
analytical study of interacting electrons in a lattice with cubic anharmonicity
are compared with the numerical simulations of two electrons in an anharmonic
lattice taking into account of the (local) Hubbard electron-electron repulsion.
We qualitative agreement between both approaches for a broad interval of
parameter values. For illustration we give expressions for the bisolectron
binding energy with parameter values that are typical for biological
macromolecules. We estimate critical values of Coulomb repulsion where the
bisolectron becomes unbound.
