“…In the present study, applying the improved Rayleigh-SchrΓΆdinger perturbation theory based on an integral equation to helium-like ions in ground states and treating electrons as perturbations, [33,34] we employ the improved variational-perturbation method (VIPM) based on the integral equation to solve the heavy quarkonium in the 2π state. [35] We apply the VIPM to the hydrogen atom in a strong and uniform magnetic field, [36] construct corrected wave functions and calculate energy corrections for ground state and some excited states such as 4π2, 4π1, 4π0, 4π.1, 4π.2, 4π 3, 4π 2, β’ β’ β’. These values are compared with those of the elaborate calculations of Smith et al [10] and the simple basis variational calculations of Jason.…”