In this study, the interaction energy (Eint) of suvorexant (as an orexin receptor antagonist) and some of its analogues with the important residues of the human OX2 orexin receptor, determined by molecular docking, is calculated using the symmetry-adapted perturbation theory-density functional theory (SAPT (DFT)) method. Also, the important residues with the dominant interaction with each ligand are determined based on the obtained SAPT (DFT) interaction energies. To analyze the interaction of the receptor with each ligand, the decomposition of Eint to its constituent components including electrostatic (Eele), exchange (Eex), induction (Eind), and exchange-induction (Eex-ind), dispersion (Edisp), and exchange-dispersion (Eex-disp) is performed. The change of interaction energy components with the replacement of the benzoxazole part of suvorexant by pyrimidine containing different functional groups, thieno pyrimidine, and furo pyrimidine is also investigated, separately. It is found that the change in Eint, due to these replacements, is controlled more by the variation of the electrostatic interaction energy component of Eint than by the other interaction energy components. A linear correlation (R2 = 0.91) is found for the variation of Eint versus experimental ligand-binding affinities. Also, the existence of the linear correlation for the variation of the interaction energy components with experimental ligand-binding affinities is investigated. The variation of the electrostatic component versus experimental ligand-binding affinities shows a more linear correlation compared to the other interaction energy components.