Moving breathers in a DNA model with competing short- and long-range dispersive interactions

Moving breathers is a means of transmitting information in DNA. We study the existence and properties of moving breathers, in a DNA model with short-range interaction, due to the stacking of the base pairs, and long-range interaction, due to the finite dipole moment of the bond within each base pair. In our study, we have found that mobile breathers exist for a wide range of the parameter values, and the mobility of these breathers is hindered by the long-range interaction. This fact is manifested by: (a) an increase of the effective mass of the breather with the dipole-dipole coupling parameter; (b) a poor quality of the movement when the dipole-dipole interaction increases; (c) the existence of a threshold value of the dipole-dipole coupling above which the breather is not movable. An analytical formula for the boundaries of the regions where breathers are movable is calculated. Concretely, for each value of the breather frequency, one can obtain the maximum value of the dipole-dipole coupling parameter and the maximum and minimum values of the stacking coupling parameter where breathers are movable. Numerical simulations show that, although the necessary conditions for the mobility are fulfilled. breathers are not always movable. Finally, the value of the dipole-dipole coupling constant is obtained through quantum chemical calculations. They show that the value of the coupling constant is small enough to allow a good mobility of breathers. (C) 2002 Elsevier Science B.V. All rights reserved.