Recently, the ferroelectric Eu0.5Ba0.5TiO3 was suggested for experimental searches of the electron electric dipole moment. To analyze results of the experiment and interpret them in terms of fundamental constants, the effective electric field E-eff acting on unpaired electrons of the europium cation should be calculated. In the present paper we consider Eu2+ cation in the uniform external electric field E-ext as the first step and important starting point toward the calculation of E-eff in the real solid. We have performed high-level electronic structure correlation calculations using the coupled clusters theory compared to other approaches. The calculated value of the field enhancement coefficient is K = E-eff/E-ext = -4.6.