The properties of polaron of crystals influence the optical properties of the crystals very remarkably. With the development of magneto-optical technology

the properties of the polaron for polar crystals in magnetic field have been of considerable interest. Zorkani et al. calculated the ground state energy of bound magnetopolaron using variational method. Employing Haga’s perturbation method

Hu et al. derived an effective Hamiltonian for the interface magnetopolaron in polar crystals to zero temperature. Kandemir et al. discussed the ground-state and first-excited-state energy of two-dimensional large magnetopolaron by using recently introduced squeezed Landau states. The effective mass of magnetopolaron in polar crystals was investigated by means of a linear-combination operator and a perturbation method by one of the authors. Most polar crystals are diatomic and cubic and their crystal structure belongs to NaCl

CsCl or ZnS type. In these crystals there is one mode of the longitudinal optical (LO) phonon. The properties of crystals have been studied by a great variety of techniques

in the case of crystals having only one LO phonon branch. However

a large number of polar crystals

with several atoms per unit cell

have more than one LO phonon branch. For example

in cuprite such as CuO

2

there are two LO phonon modes. Si

2

GaAs

1-x

P

x

and a large number of perovskites (SrTiO

3

BaTiO

3

LiNbO

3

ets.) have more than two modes. In recent years

the polaron problem with many LO phonon branches has been investigated. The properties of the polaron in polyatomic polar crystals are studied using a linear-combination operator method by one of the authors. However

the magnetopolaron in polyatomic polar crystals has not been investigated so far. Recently

Wei and co-workers studied the properties of strong-coupling surface magnetopolaron in polyatomic polar crystals. In this paper

the properties of the bulk polaron for polyatomic polar crystals in magnetic field are studied. The ground state energy of a strong-and weak-coupling bulk polaron in polyatomic polar crystals are derived by the method of a linear-combination operator.