In this paper, we develop Schiffs discretization procedure for calculating the phase shifts in the hq54 model in (D + 1 )-dimensional space-time (D > 0) with the Gaussian wave-functional approach. In 1 + 1 and 2+ 1 dimensions, the phase shifts are negative, which indicates the interaction between two pions is repulsive. In 3+ 1 dimensions, the phase shifts vanish. We also discuss the dependences of the phase shifts upon the scattering energy in detail.PACS number(s): 11.80.Fv, 11.80.EtThe scattering process serves as a major source of information about the properties of various elementary particles, while the phase shift is a crucial quantity characterizing this process. Traditionally, the scattering problem is coped with mainly by the covariant perturbation technique. Recently, however, the development of the Gaussian wave-functional (GWF) approach has hinted that it is possible to analytically calculate the phase shift in quantum field theory. In the last decade, the Gaussian wave-functional approach in the Schrodinger picture field theory which was gradually developed by Schiff [I], Rosen [2], Barnes and Ghandour [3], etc., has become a powerful tool for investigating the vacuum structure [4-101 as well as searching for the bound states in quantum field theory [5,11,12]. Being explicitly computed, the two-particle state energy may be analyzed to extract knowledge on the phase shift. As an attempt, we have investigated the scattering state in the sinh-Gordon and the sine-Gordon models with this approach [13,14]. In this Brief Report, we continue to study the simplest selfcoupling model, the h44 model, with the same approach.The model was originally introduced into quantum field theory to describe the pion-pion interaction [1,1S]. By now it has become an important model in quantum field theory (including gauge theory), finite-temperature field theory, quantum cosmology, and condensed-matter physics. This model is also an ideal theoretical laboratory for various new methods. Since being advocated [16], the Gaussian wave-functional approach has been used for many problems in ~4~ theory, such as spontaneous symConsider a scalar field 4(x)=4, [ x = ( x l , x 2 , . . . ,x,)is the coordinate in D-dimensional space] described by the Hamiltonian where J x = Jdx = Jdx l d~Z . . dxD and V is the gradient operator in D-dimensional space. m and h are the bare mass and coupling parameters, respectively.From [3,4], the Gaussian vacuum state is where y,z = I dy dz = I d y ,dy2 -. dyDdz ,dz2 . . dz,,