Epitaxial integration of III-V semiconductors on silicon substrate has been of great interest over the years for different applications in photovoltaics, microelectronics, and water splitting applications. The performance of the device is challenged by surfaces and interfaces[1-2]but also by anti-phase boundaries[3-5] (APBs). APBs present a great challenge both during growth and later by directly affecting the electronic properties[5] of the heterostructure. There are many types of APBs and they can be further categorized on the basis of their orientations. Historically, it has been assumed that the GaP/Si abrupt interface formation coupled by the growth of stoichiometric(110) APB is the most favorable[6-7]. However, recent experimental results contradict the theoretical assumption[1]. For different GaP/Si interfaces, compensated GaP/Si interface is shown to be more stable[8]. In this study, the growth of GaP on the monoatomic Si step has been studied. We used density functional theory (DFT) to determine the excess energies in the heterostructures. Results of the study reveal that for various GaP/Si(001) heterostructures, the excess energy contributing to compensated GaP/Si interface without stoichiometric APB is the most stable growth scenario while the abrupt GaP/Si interface including the growth of stoichiometric APB is the most unstable. References: [1] I. Lucci et al., Physical Review Materials 2 (6), 060401, 2018 [2] I. Lucci et al., Advanced Functional Materials, 28(30):1801585, 2018 [3] L. Chen et al., ACS Nano 14, 13127, 2020 [4] L. Chen et al., Advanced Science, 9, 2101661, 2022 [5] L. Chen, et al., Physical Review B 106 (16), 165310, 2022 [6] H. Kroemer. Polar-on-nonpolar epitaxy, 81(1-4), 193–204, 1987 [7] O. Rubel et al., Int. J. Mol. Sci, 10(12), 2009 [8] S. Pallikkara Chandrasekharan et al., Physical Review B 108, 075305, 2023