EN
Perturbation methods are generally used for solving wave operator equations associated with the determination of effective Hamiltonians. In many cases the standard Rayleigh-Schrodinger and Brillouin-Wigner series either converge slowly or diverge. Therefore it is necessary to modify or to renormalize the standard wave equations. For that purpose derivative and convergence superoperators within the Ralyeigh-Schrodinger and Brillouin-Wigner formalisms were introduced. A new efficient otential is obtained and further application to molecular dynamics is indicated.