The interaction energy between rutile TiO2 (1 1 0) surface and CO2 molecule has been investigated by ab initio quantum chemical calculations in order to increase the adsorption energy between the surface and the adsorbate by a chemical modification of the surface. In this work, we propose a novel approach for chemical modifications by utilizing the ab initio calculations. The interaction energy between a surface and a molecule can be decomposed into several physically meaningful terms such as electrostatic, polarization and charge transfer interactions by the Kitaura-Morokuma analysis. In the case when the charge transfer interaction from the molecule to surface is dominant, replacing several Ti atoms by the element that has larger electron negativity than the Ti atom will be appropriate. Such modification will promote the charge transfer from molecule to surface, which will leads to the increase in the stabilization energy. We represent TiO2 surface by a Ti7O22H16 cluster in which dangling bonds are terminated by hydrogen atoms. Geometry optimizations as well as the Kitaura-Morokuma analysis are performed within the RHF level for the CO2 and Ti7O22H16 system. In the CO3 form adsorption geometry, the charge transfer interaction energy from the cluster to CO2 is found to be dominant among the component interactions. It is demonstrated that replacement of two Ti atoms by two Ca atoms drastically promotes the charge transfer in accord with our proposal and consequently, the total adsorption energy increases. The mechanism of the increase in the charge transfer interaction as well as CO2 adsorption on the TiO2 cluster is discussed by investigating the spacial distribution of the HOMO electron density of the cluster.