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We investigate the multidomain structures in the tetragonal and orthorhombic phases of BaTiO3 and the impact of the presence of domain walls on the intermediary phase transition. We focus on the change in the transition temperatures resulting from various types of domain walls and their coupling with an external electric field. We employ molecular dynamics simulations of an ab initio effective Hamiltonian in this study. After confirming that this model is applicable to multidomain configurations, we show that the phase-transition temperatures strongly depend on the presence of domains walls. Notably we show that elastic 90° walls can strongly reduce thermal hysteresis. Further analysis shows that the change in transition temperatures can be attributed to two main factors: long-range monoclinic distortions induced by walls within domains and domain wall widths. We also show that the coupling with the field further facilitates the reduction of thermal hysteresis for orthorhombic 90° walls, making this configuration attractive for future applications.