Efficient CO₂ capture by ionic liquids needs a thorough understanding of underlying mechanisms of the CO₂ interaction with ionic liquids, especially when it involves chemisorption. In this work we have systematically investigated the mechanism of CO₂ capture by 1,3 di-substituted imidazolium acetate ionic liquids using density functional theory. Solvent effects are analyzed using QM/MM and QM/QM approaches with the help of molecular dynamics simulations and ONIOM methods. The investigation of different stepwise mechanisms shows that CO₂ could be involved in the first step of the reaction mechanism, also a new two-step mechanism is proposed. The final stabilization step is analyzed and pointed out to be responsible for important experimentally-observed features of the reaction.