Calculations of site-specific CO stretching frequencies for copper carbonyls with the "near spectroscopic accuracy":: CO interaction with Cu+/MFI

A scaling method based on the linear correlation between the CO bond length and the CO stretching frequency has been applied to the CO molecule adsorbed on the Cu-exchanged MFI zeolite. Effects of anharmonicity, cluster size, unit cell size, and the Madelung potential were investigated. Interaction of CO with zeolite framework was described at the combined RI-BLYP/IPF level. The inner part of the combined model (RI-BLYP description) consisted of up to 23 TO4 tetrahedra. The effect of the Madelung potential on CO stretching frequencies was negligible. All Cu+ sites on the channel intersection and on the wall of the main channel are characterized by the CO stretching frequencies in the narrow range of 2159-2164 cm(-1) in excellent agreement with experimental data. The Cu+ sites on the wall of the zigzag channel show slightly higher frequencies (3 - 6 cm(-1)). These sites are populated, however, only when the framework Al atoms are at T4 or T10 positions. The proposed computational scheme provides essentially the same level of accuracy as obtained from CCSD(T) calculations for small copper carbonyl species with overall error smaller than 5 cm(-1).