We will present the development of the correlation consistent composite approach (ccCA) to the calculation of first and second energy derivatives (gradients and Hessian matrices). The ccCA method attempts to emulate the expensive high-level <i>ab initio</i> methods by combining different methods with the much lower computational cost. Starting from an electron correlation method that is not quite computationally demanding, various corrections are added (e.g., higher-level correlation methods, core-valence interactions, relativistic effects, etc.) at a relatively low basis set, and it could eventually reach very high accuracy. However, among all the versions of ccCA methods that are currently implemented, none of them could calculate anything beyond the single point energies.<br/><br/>Recent development has made the ccCA method moved one step further. Beside the single point energies, now it is also capable of calculating the first and second energy derivatives which can be applied to many important properties such as geometries and harmonic vibrational frequencies. Compared to the benchmark results calculated by the CCSD(T) at the large basis set, ccCA method could generate the similar results but has significantly reduced computational cost. This presentation will focus on the principles of ccCA energy derivatives and the results for the main group elements.

Beyond the single point energies: Incorporating the correlation consistent composite approach to the energy derivatives

256th National Meeting (2018)

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