The Counterpoise Correction method used for the basis set superposition effect is failed; where and why?

초록

Nowadays, small metal clusters are widely used as catalysts owing to their unique catalytic properties. On the other hand, exploring a suitable bimetallic catalyst for the specific reaction from a pool of homotops is remain a challenging task. To ease this situation, for the initial screening of the catalysts theoretical calculations have been used; for this purpose, adsorption energy (Sabatier’s principal) is used as the primary predictor for the catalytic activities. While calculating the intermolecular interactions with finite basis sets we must have to face the basis set superposition effect (BSSE). Owing to BSSE, calculated complexation energies are overestimated; therefore, for accurate measurement of interactions, removal of BSSE is inevitable. Multiple procedures have been designed (using infinite basis set?practically not feasible, chemical Hamiltonian approach?some technical hurdle to apply, self-consistent field for molecular interactions?overcorrect BSSE and counterpoise method) to overcome this problem, a posterior counterpoise correction (CP) method, in this procedure ghost orbitals of partner fragment is used, implemented in different software has been applied extensively. One might expect that CP correction will always weaken the binding interaction, which justifies the variational principle. In contrast, we did not find this trend in all the systems studied here. To unravel the cause of this failure we have performed the systematic study. First, we have confirmed the compatibility of B3PW91 functional with CP method for transition metal clusters because earlier, non-compatibility of some exchange-correlation (XC) functionals were reported. MP2 calculations unravel that this failure is not attributed to the breakdown of XC functionals. Further work explores that, like XC functionals, making basis set empirical may also lead the other theoretical practices meaningless or non-compatible.