Sanibel Symposium

 

This presentation will present the recently developed correlation-consistent composite approach (ccCA) based on the distinguishable cluster approximation especially its application to the systems with strong multireference characters. As a composite method, ccCA could compute the thermochemical properties with the accuracy comparable to the high-level ab initio methods at large basis sets. At the same time, it could significantly reduce the computational cost. But the traditional ccCA is not capable to correctly describe those systems that the multireference character is significant. Also, due to the bottleneck of CCSD(T) calculation, the overall cost may still be large.

The new ccCA method, that is, ccCA-D, is a composite approach designed by replacing the coupled-cluster method in the traditional ccCA formula to the distinguishable cluster approximation while maintaining all other features. It is still designed based on the single configurational reference state, but it is able to correctly describe some systems with strong multireference characters such as the triple bond dissociation of the nitrogen molecule. At the same time, it could further reduce the computing time while maintaining a similar accuracy. The benchmark studies have demonstrated that the accuracy of the new method in predicting the thermochemical properties – both the main group elements and transition metal systems – is comparable to the traditional ccCA methods which are more expensive. In this presentation, the principles, applications, benefits, and limitations of the new method will be presented.